Method and apparatus for reference signal configurations for CSI-RS port sharing in mobile communication system using massive array antennas

ABSTRACT

A communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT) are provided. The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. According to embodiments of the present disclosure, The system includes a base station having a large number of transmission antennas of a two dimensional (2D) antenna array structure can prevent excessive feedback resource allocation for transmitting channel state information reference signals (CSI-RSs) and increase of channel estimation complexity of a terminal, and the terminal can effectively measure channels of a large number of transmission antennas and can report to the base station feedback information configured through the measurement.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 16/206,378, filed on Nov. 30, 2018, which has issued as U.S. Pat.No. 10,498,424 on Dec. 3, 2019, which was a continuation application ofprior application Ser. No. 15/664,641, filed on Jul. 31, 2017, whichissued as U.S. Pat. No. 10,148,334, on Dec. 4, 2018, and was based onand claimed priority under 35 U.S.C § 119(a) of a Korean patentapplication number 10-2016-0097558, filed on Jul. 29, 2016, in theKorean Intellectual Property Office, the disclosure of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a general wireless mobilecommunication system. More particularly, the present disclosure relatesto a method for transmitting and receiving channel state information, inwhich a terminal measures wireless channel quality and reports themeasurement result to a base station with respect to signals that aretransmitted using various virtualization from a plurality of basestations using a plurality of active array antennas in a wireless mobilecommunication system that applies a multiple access scheme using amulticarrier, such as an orthogonal frequency division multiple access(OFDMA).

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of fourth generation (4G) communication systems, efforts havebeen made to develop an improved fifth generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post long term evolution(LTE) System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), full dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud radio access networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,coordinated multi-points (CoMP), reception-end interference cancellationand the like. In the 5G system, hybrid frequency shift keying (FSK) andquadrature amplitude modulation (QAM) modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology,”“wired/wireless communication and network infrastructure,” “serviceinterface technology,” and “Security technology” have been demanded forIoT implementation, a sensor network, a machine-to-machine (M2M)communication, machine type communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies, suchas a sensor network, MTC, and M2M communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud radioaccess network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method for configuring channel stateinformation reference signals (CSI-RSs) having various numbers ofantenna ports to support a full dimensional multiple-inputmultiple-output (FD-MIMO) system having various antenna array shapes.

Another aspect of the present disclosure is to provide a base stationconfigure and transmit {1, 2, 4, 8, 12, 16, 24, 32} numbered CSI-RSs toterminals to suit its own antenna array shape. On the other hand, aterminal may have a limited number of CSI-RS ports for receiving theCSI-RSs in accordance with the release of the terminal. For example, inthe case where there are terminals having different releases in onecell, the reception abilities of the respective terminals may differfrom one another in a manner that some terminals may receive CSI-RSshaving maximally up to 8 ports, other terminals may receive CSI-RSshaving maximally up to 16 ports, and the remaining terminals may receiveCSI-RSs having maximally up to 32 ports.

In accordance with an aspect of the present disclosure, a method for abase station is provided. The method includes transmitting CSI-RSconfiguration information to a terminal, transmitting feedbackconfiguration information, generating CSI-RSs based on the CSI-RSconfiguration information to transmit the CSI-RSs, and receiving CSIbased on the feedback configuration information wherein the CSI-RSs aretransmitted using a plurality of antenna ports, and a number of aplurality of antenna ports is determined in accordance with antennaarray configurations included in reference CSI-RS configurations.

In accordance with another aspect of the present disclosure, a methodfor a terminal is provided. The method includes receiving CSI-RSconfiguration information from a base station, receiving feedbackconfiguration information, receiving CSI-RSs based on the CSI-RSconfiguration information, and transmitting CSI generated based on thefeedback configuration information and the CSI-RSs, wherein the CSI-RSsare transmitted using a plurality of antenna ports, and a number of aplurality of antenna ports is determined in accordance with antennaarray configurations included in reference CSI-RS configurations.

In accordance with another aspect of the present disclosure, a basestation is provided. The base station includes a transceiver configuredto transmit and receive signals with a terminal, and a controllerconfigured to transmit CSI-RS configuration information to the terminal,transmit feedback configuration information, generate CSI-RSs based onthe CSI-RS configuration information to transmit the CSI-RSs, andreceive CSI based on the feedback configuration information, wherein theCSI-RSs are transmitted using a plurality of antenna ports, and a numberof a plurality of antenna ports is determined in accordance with antennaarray configurations included in reference CSI-RS configurations.

In accordance with another aspect of the present disclosure, a terminalis provided. The terminal includes a transceiver configured to transmitand receive signals with a base station, and a controller configured toreceive CSI-RS configuration information from the base station, receivefeedback configuration information, receive CSI-RSs based on the CSI-RSconfiguration information, and transmit CSI generated based on thefeedback configuration information and the CSI-RSs, wherein the CSI-RSsare transmitted using a plurality of antenna ports, and a number of aplurality of antenna ports is determined in accordance with antennaarray configurations included in reference CSI-RS configurations.

In accordance with another aspect of the present disclosure, a methodfor a base station is provided. The method includes transmitting CSI-RSconfiguration information to a terminal, transmitting feedbackconfiguration information to the terminal, and transmitting the CSI-RSbased on the CSI-RS configuration information, wherein an antenna portnumber of the CSI-RS transmitted to the terminal is determined based ona component CSI-RS configuration and a maximum number of CSI-RS antennaports that the terminal is capable of receiving.

In accordance with another aspect of the present disclosure, a methodfor a terminal is provided. The method includes receiving CSI-RSconfiguration information from a base station, receiving feedbackconfiguration information from the base station, and receiving theCSI-RS based on the CSI-RS configuration information, wherein an antennaport number of the CSI-RS received from the base station is determinedbased on a component CSI-RS configuration and a maximum number of CSI-RSantenna ports that the terminal is capable of receiving.

In accordance with another aspect of the present disclosure, a basestation is provided. The base station includes a transceiver configuredto transmit and receive signals, and a controller coupled with thetransceiver and configured to transmit CSI-RS configuration informationto a terminal, transmit feedback configuration information to theterminal, and transmit the CSI-RS based on the CSI-RS configurationinformation, wherein an antenna port number of the CSI-RS transmitted tothe terminal is determined based on a component CSI-RS configuration anda maximum number of CSI-RS antenna ports that the terminal is capable ofreceiving.

In accordance with another aspect of the present disclosure, a terminalis provided. The terminal includes a transceiver configured to transmitand receive signals, and a controller coupled with the transceiver andconfigured to receive CSI-RS configuration information from a basestation, receive feedback configuration information from the basestation, and receive the CSI-RS based on the CSI-RS configurationinformation, wherein an antenna port number of the CSI-RS received fromthe base station is determined based on a component CSI-RS configurationand a maximum number of CSI-RS antenna ports that the terminal iscapable of receiving.

According to the aspects of the present disclosure, a method and anapparatus for generating CSI for performing effective datatransmission/reception and sharing the generated CSI in a long termevolution-advanced (LTE-A) based FD-MIMO system. Specifically, thepresent disclosure provides a method and an apparatus in which a basestation notifies a terminal of configuration information for a pluralityof CSI-RSs and the terminal generates feedback information in accordancewith the configuration information in order to transmit and receivehigh-efficiency data in the FD-MIMO system.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a massive multi-antenna systemaccording to an embodiment of the present disclosure;

FIG. 2 is a diagram illustrating a wireless resource including onesubframe and one resource block (RB), which is a minimum unit capable ofperforming scheduling to a downlink in a long term evolution(LTE)/LTE-advanced (LTE-A) system according to an embodiment of thepresent disclosure;

FIG. 3 is a diagram illustrating a channel state information referencesignal (CSI-RS) resource element (RE) mapping for an n^(th) and(n+1)^(th) physical resource blocks (PRBs) in a case where a basestation transmits channel state information reference signals (CSI-RSs)of 8 antenna ports according to an embodiment of the present disclosure;

FIGS. 4A and 4B are diagrams illustrating CSI-RS subgroup mapping on atime axis or a frequency axis according to various embodiments of thepresent disclosure;

FIGS. 5A, 5B, and 5C are diagrams illustrating CSI-RS subgroupgeneration for full port mapping and partial port mapping in anenvironment in which 20 transceiver units (TXRUs) exist according tovarious embodiments of the present disclosure;

FIGS. 6A and 6B are diagrams illustrating partial port mapping beingperformed without CSI-RS subgroup configurations according to variousembodiments of the present disclosure;

FIG. 7 is a diagram illustrating CSI-RS configurations by comb_(T) orcomb_(F) according to an embodiment of the present disclosure;

FIG. 8 is a diagram illustrating CSI-RS resources having low overheadthat may be configured to a terminal according to an embodiment of thepresent disclosure;

FIG. 9 is a diagram illustrating CSI-RS port sharing according to anembodiment of the present disclosure;

FIG. 10 is a diagram illustrating a resource configuration for eachterminal for CSI-RS port sharing according to an embodiment of thepresent disclosure;

FIG. 11 is a diagram illustrating CSI-RS resource configuration for eachterminal when CSI-RS is configured to a terminal after release 14 withCSI-RS RE density of one RE/RB/port according to an embodiment of thepresent disclosure;

FIG. 12 is a diagram illustrating CSI-RS resource configuration and portnumbering if CSI-RS RE density for a larger number of CSI-RS ports isdifferent from CSI-RS RE density for a small number of CSI-RS portsaccording to an embodiment of the present disclosure;

FIG. 13 is a diagram illustrating a base station array being decomposedinto subgroups in a horizontal direction and CSI-RS virtualization isperformed with respect to the decomposed subgroups according to anembodiment of the present disclosure;

FIG. 14 is a diagram illustrating CSI-RS resource configuration and portnumbering if CSI-RS RE density for a larger number of CSI-RS ports isdifferent from CSI-RS RE density for a small number of CSI-RS portsaccording to an embodiment of the present disclosure;

FIG. 15 is a diagram illustrating a base station array being decomposedinto subgroups in a vertical direction and CSI-RS virtualization isperformed with respect to the decomposed subgroups according to anembodiment of the present disclosure;

FIGS. 16 and 17 are diagrams illustrating port sharing between CSI-RSsusing an orthogonal cover code of length 4 (CDM-4) according to anembodiment of the present disclosure;

FIG. 18 is a flowchart illustrating an order of operations of a terminalaccording to an embodiment of the present disclosure;

FIG. 19 is a flowchart illustrating an order of operations of a basestation according to an embodiment of the present disclosure;

FIG. 20 is a block diagram illustrating an internal structure of aterminal according to an embodiment of the present disclosure; and

FIG. 21 is a block diagram illustrating an internal structure of a basestation according to an embodiment of the present disclosure.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

In this case, it may be understood that each block of processing flowcharts and combinations of the flow charts may be performed by computerprogram instructions. Since these computer program instructions may bemounted in processors for a general computer, a special computer, orother programmable data processing apparatuses, these instructionsexecuted by the processors for the computer or the other programmabledata processing apparatuses create means performing functions describedin block(s) of the flow charts. Since these computer programinstructions may also be stored in a computer usable or computerreadable memory of a computer or other programmable data processingapparatuses in order to implement the functions in a specific scheme,the computer program instructions stored in the computer usable orcomputer readable memory may also produce manufacturing articlesincluding instruction means performing the functions described inblock(s) of the flow charts. Since the computer program instructions mayalso be mounted on the computer or the other programmable dataprocessing apparatuses, the instructions performing a series ofoperation steps on the computer or the other programmable dataprocessing apparatuses to create processes executed by the computer tothereby execute the computer or the other programmable data processingapparatuses may also provide steps for performing the functionsdescribed in block(s) of the flow charts.

In addition, each block may indicate some of modules, segments, or codesincluding one or more executable instructions for executing a specificlogical function(s). Further, it is to be noted that functions mentionedin the blocks occur regardless of a sequence in some alternativeembodiments. For example, two blocks that are consecutively illustratedmay be simultaneously performed in fact or be performed in a reversesequence depending on corresponding functions sometimes.

Here, the term ‘˜unit’ used in the present embodiment means software orhardware components such as FPGA and ASIC and the ‘unit’ performs anyroles. However, the meaning of the ‘unit’ is not limited to software orhardware. The ‘˜unit may be configured to be in a storage medium thatmay be addressed and may also be configured to reproduce one or moreprocessor. Accordingly, for example, the’˜unit includes components suchas software components, object oriented software components, classcomponents, and task components and processors, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuit, data, database, data structures, tables, arrays, andvariables. The functions provided in the components and the ‘˜units’ maybe combined with a smaller number of components and the ‘˜units’ or mayfurther be separated into additional components and ‘˜units’. Inaddition, the components and the ‘˜units’ may also be implemented toreproduce one or more CPUs within a device or a security multimediacard.

In describing embodiments of the present disclosure, although anorthogonal frequency division multiplexing (OFDM)based wirelesscommunication system, in particular, the 3^(rd)(generation partnershipproject (3GPP) Evolved Universal Terrestrial Radio Access (EUTRA)standard, will be the primary subject, the main gist of the presentdisclosure can be applied to other communication systems having similartechnical backgrounds and channel types with slight modifications withina range that does not greatly deviate from the scope of the presentdisclosure, by the judgment of those skilled in the art to which thepresent disclosure pertains. The aspects and features of the presentdisclosure and methods for achieving the aspects and features will beapparent by referring to the embodiments to be described with referenceto the accompanying drawings.

However, the present disclosure is not limited to the embodimentsdisclosed hereinafter, but can be implemented in diverse forms. Thematters defined in the description, such as the detailed constructionand elements, are nothing but specific details provided to assist thoseof ordinary skill in the art in a comprehensive understanding of thedisclosure, and the present disclosure is only defined within the scopeof the appended claims. In the entire description of the presentdisclosure, the same drawing reference numerals are used for the sameelements across various figures.

At present, a mobile communication system has been developed to ahigh-speed and high-quality wireless packet data communication system inorder to provide massive data services and multimedia services overinitial voice oriented services. Several standardization groups, such as3GPP and Institute of Electrical and Electronics Engineers (IEEE), areproceeding with 3rd-generation evolved mobile communication systemstandards adopting a multicarrier based multiple access method in orderto satisfy such requirements. As a result, various mobile communicationstandards, such as 3GPP long term evolution (LTE) advanced (LTE-A) andIEEE 802.16m, have been developed to support high-speed and high-qualitywireless packet data transmission services based on a multiple accessmethod using multi-carriers.

As described above, the existing 4th-generation evolved mobilecommunication systems, such as LTE-A and 802.16m, are based on themulti-carrier multiple access method, and use various technologies, suchas multiple input multiple output (MIMO, multi-antenna), beam-forming,adaptive modulation and coding (AMC), and channel sensitive scheduling,in order to improve the transmission efficiency. The varioustechnologies as described above increase the system capacity performanceby improving the transmission efficiency through methods forconcentrating transmission powers transmitted from several antennas,adjusting the amount of data being transmitted, and selectivelytransmitting data to users having good channel quality, using variouskinds of channel state information (CSI).

Since such techniques mostly operate based on CSI between a base station(BS) (that may be mixedly used with an evolved Node B (eNB)) and aterminal (that may be mixedly used with a user equipment (UE) and amobile station (MS)), it is necessary for the eNB or the UE to measure achannel state between the base station and the terminal, and in thiscase, a channel state information reference signal (CSI-RS) is used. Theabove-described eNB indicates a downlink transmission and uplinkreception device located in a certain place, and one eNB can performtransmission/reception for a plurality of cells. In one mobilecommunication system, a plurality of eNBs are geometrically distributed,and each of the plurality of eNBs performs transmission/reception for aplurality of cells.

The existing 3rd-generation and 4th-generation mobile communicationsystems, such as LTE/LTE-A, use MIMO technology to transmit data using aplurality of transmission/reception antennas for extension of the datatransmission speed and system capacity. The MIMO technology makes itpossible to spatially separate and transmit a plurality of informationstreams using a plurality of transmission/reception antennas, and suchspatial separation and transmission of the plurality of informationstreams may be called spatial multiplexing. In general, how manyinformation streams spatial multiplexing can be applied to is defined asa rank of the corresponding transmission, and this rank differsdepending on the number of antennas of a transmitter and a receiver. Inthe case of the MIMO technology that is supported in the standards up toLTE/LTE-A Release 12, spatial multiplexing is supported with respect tocases where 2, 4, and 8 transmission/reception antennas are respectivelyprovided.

In contrast, a massive multi-antenna (massive MIMO) system or afull-dimension MIMO (FD-MIMO) system, to which the technology proposedin the present disclosure is applied, includes 8 or more antennas thatare two-dimensionally arranged.

FIG. 1 is a diagram illustrating a massive multi-antenna systemaccording to an embodiment of the present disclosure.

Referring to FIG. 1, a base station transmission equipment 101 transmitsa wireless signal using not less than several tens of transmissionantennas. As illustrated in FIG. 1, the plurality of transmissionantennas are deployed to maintain a certain distance between them. Thecertain distance may correspond to, for example, a multiple of a half ofa wavelength of a wireless signal being transmitted. In general, if thedistance corresponding to a half of the wavelength of the wirelesssignal is maintained between the transmission antennas, signalstransmitted from the respective transmission antennas are affected bywireless channels having low correlation between them. As the distancebetween the transmission antennas becomes longer, the correlationbetween the signals becomes lower.

In the base station transmission equipment 101 having massive antennas,in order to prevent the scale of the equipment from becoming extremelylarge, the antennas may be two-dimensionally arranged as illustrated inFIG. 1. In this case, a base station transmits signals using NH antennasarranged on a horizontal axis and N_(V) antennas arranged on a verticalaxis, and a terminal 103 should measure channels 102 for thecorresponding antennas.

In FIG. 1, not less than several tens of transmission antennas arrangedon the base station transmission equipment 101 are used to transmitsignals to one or a plurality of terminals. Proper precoding may beapplied to a plurality of transmission antennas to simultaneouslytransmit signals to a plurality of terminals. In this case, one terminalmay receive one or more information streams. In general, the number ofinformation streams that one terminal can receive is determined inaccordance with the number of reception antennas that the terminalpossesses and the channel state.

In order to effectively implement the massive multi-antenna system, itis necessary for a terminal to accurately measure the channel statebetween transmission/reception antennas and the size of interferenceusing a plurality of reference signals and to transmit to a base stationeffective CSI generated using them. The base station that has receivedthe CSI determines what terminals it performs transmission to inrelation to signal transmission of a downlink, at what data transmissionspeed it performs transmission, and what proceedings it applies. TheFD-MIMO system has a large number of transmission antennas, and if amethod for transmitting and receiving CSI of the LTE/LTE-A system in therelated art is applied, it is necessary to transmit a large amount ofcontrol information to cause an uplink overhead problem.

In a mobile communication system, time, frequency, and power resourcesare limited. Accordingly, if a larger amount of resources is allocatedto reference signals, resources to be allocated to traffic channeltransmission for transmitting data are reduced to cause an absoluteamount of data to be transmitted also to be reduced. In this case, thechannel measurement and estimation performance may be improved, but anabsolute amount of data to be transmitted is reduced, and thus, thewhole system capacity performance may be rather deteriorated.

Accordingly, in order to derive an optimum performance on the side ofthe whole system capacity, proper distribution is necessary betweenresources for reference signals and resources for traffic channeltransmission.

FIG. 2 is a diagram illustrating a wireless resource including onesubframe and one resource block (RB), which is a minimum unit capable ofperforming downlink scheduling in an LTE/LTE-A system according to anembodiment of the present disclosure.

Referring to FIG. 2, a wireless resource including one subframe on atime axis and one RB on a frequency axis is illustrated. The wirelessresource includes 12 subcarriers in a frequency domain and 14 OFDMsymbols in a time domain to have 168 inherent frequency and timelocations in total. In the LTE/LTE-A, each of the inherent frequency andtime locations as shown in FIG. 2 is called a resource element (RE).

From the wireless resources as illustrated in FIG. 2, different kinds ofplural signals may be transmitted as follows.

1. Cell specific RS (CRS): A reference signal periodically transmittedfor all terminals belonging to one cell. A plurality of terminals maycommonly use the CRS.

2. Demodulation reference signal (DMRS): A reference signal transmittedfor a specific terminal. The DMRS is transmitted only in the case wheredata is transmitted to the corresponding terminal. The DMRS may beincluding 8 DMRS antenna ports (hereinafter referred to as “port,” whichcan be mixedly used with an SP) in total. In the LTE/LTE-A, ports 7 to14 correspond to DMRS ports, and the respective ports maintainorthogonality so that no interference occurs between them using codedivision multiplexing (CDM) or frequency division multiplexing (FDM).

3. Physical downlink shared channel (PDSCH): A data channel transmittedto a downlink. The PDSCH is used by a base station to transmit trafficto a terminal, and it is transmitted using an RE in which a referencesignal is not transmitted through a data region of FIG. 2.

4. CSI-RS: A reference signal transmitted for terminals belonging to onecell. The CSI-RS is used to measure a channel state. A plurality ofCSI-RSs may be transmitted to one cell.

5. Other control channels (physical hybrid automatic-repeat-request(HARQ) indicator channel (PHICH), physical control format indicatorchannel (PCFICH), and physical downlink control channel (PDCCH)): Thesecontrol channels are used to provide control information that isnecessary for a terminal to receive the PDSCH or to transmitacknowledgement (ACK)/negative acknowledgement (NACK) for operating HARQfor data transmission of an uplink.

In addition to the above-described signals, in the LTE-A system, mutingmay be configured so that CSI-RSs transmitted by other base stations canbe received in terminals of the corresponding cell without interference.The muting may be applied in a location in which CSI-RSs can betransmitted, and in general, a terminal receives a traffic signalthrough jumping over the corresponding wireless resource. In the LTE-Asystem, the muting may be called zero-power CSI-RS as another term. Thisis because due to the characteristic of the muting, the muting isapplied to the location of the CSI-RS in the same manner and there isnot transmission power of the corresponding wireless resource.

Referring to FIG. 2, the CSI-RSs may be transmitted using parts oflocations indicated as A, B, C, D, E, E, F, G, H, I, and J in accordancewith the number of antennas that transmit the CSI-RSs. Further, themuting may be applied to parts of the locations indicated as A, B, C, D,E, E, F, G, H, I, and J. In particular, the CSI-RSs may be transmittedto 2, 4, and 8 Res in accordance with the number of antenna ports beingtransmitted. In FIG. 2, if the number of antenna ports is 2, the CSI-RSsare transmitted to a half of a specific pattern, whereas if the numberof antenna ports is 4, the CSI-RSs are transmitted to the whole of thespecific pattern. If the number of antenna ports is 8, the CSI-RSs aretransmitted using two patterns. In contrast, the muting is alwaysperformed in one pattern unit. For example, the muting may be applied toa plurality of patterns, but if the location of the muting does notoverlap the location of the CSI-RS, it cannot be applied to only a partof one pattern. However, only in the case where the location of theCSI-RS overlaps the location of the muting, the muting can be applied toonly a part of one pattern.

In the case where the CSI-RSs for two antenna ports are transmitted, twoREs connected together on a time axis transmit signals of respectiveantenna ports, and the signals of the respective antenna ports arediscriminated from one another by orthogonal codes. Further, if theCSI-RSs for four antenna ports are transmitted, signals for the tworemaining antenna ports are transmitted in the same method further usingtwo REs added to the CSI-RSs for the two antenna ports. Transmission ofthe CSI-RSs for 8 antenna ports is performed in the same manner.

In order to improve accuracy of channel estimation, a base station mayboost the transmission power of the CSI-RSs. If the CSI-RSs for 4 or 8antenna ports (APs) are transmitted, specific CSI-RS ports aretransmitted from only the CSI-RS RE in a certain location in the sameOFDM symbol, but they are not transmitted from other OFDM symbols.

FIG. 3 is a diagram illustrating CSI-RS RE mapping for an n^(th) and(n+1)^(th) physical resource blocks (PRBs) in a case where a basestation transmits CSI-RSs of 8 antenna ports according to an embodimentof the present disclosure.

Referring to FIG. 3, if the CSI-RS RE location for an AP 15 or 16 is asshown as 310 in FIG. 3, transmission power for the AP 15 or 16 is notused in a CSI-RS RE 320 for the remaining APs 17 to 22. Accordingly, asindicated in FIG. 3, the AP 15 or 16 may use transmission power to beused for the 3rd, 8th, and 9th subcarriers in the 2nd subcarrier. Suchnatural power boosting enables the transmission power of a CSI-RS port15 transmitted through the 2nd subcarrier to be highly configuredmaximally up to 6 dB as compared with the transmission power of a dataRE 300. According to the current 2/4/8 port CSI-RS patterns, naturalpower boosting of 0/3/6 dB becomes possible, and through this, therespective APs can transmit CSI-RSs with full power utilization.

Further, a terminal can be allocated with CSI-interference measurements(IMs) (or interference measurement resources (IMRs)) together with theCSI-RSs, and the CSI-IM resources have the same resource structure andlocation as those of the CSI-RSs supporting 4 ports. The CSI-IM is aresource for a terminal that receives data from one or more base stationto accurately measure interference with an adjacent base station. Forexample, if it is desired to measure the amount of interference when theadjacent base station transmits data and the amount of interference whenthe adjacent base station does not transmit the data, the base stationconfigures a CSI-RS and two CSI-IM resources, the base station caneffectively measure the amount of interference exerted by the adjacentbase station in a manner that it makes the adjacent base station alwaystransmit a signal on one CSI-IM whereas it makes the adjacent basestation always not transmit the signal on the other CSI-IM.

In the LTE-A system, the base station may report CSI-RS configurationinformation to the terminal through higher layer signaling. The CSI-RSconfiguration information includes an index of CSI-RS configurationinformation, the number of antenna ports included in a CSI-RS, atransmission period of the CSI-RS, a transmission offset, CSI-RSresource configuration information, CSI-RS scrambling, and quasico-location (QCL).

In the cellular system, the base station should transmit a referencesignal to the terminal in order to measure a downlink channel state, andin the case of the 3GPP LTE-A system, the terminal measures a channelstate between the base station and the terminal itself using the CRS orCSI-RS transmitted from the base station. The channel state basicallyhas some requisites that should be considered, and here, it includes theamount of interference in a downlink. The amount of interference in thedownlink includes an interference signal and thermal noise generated byantennas that belong to the adjacent base station, and it plays animportant role in determining the channel situation of the downlink.

As an example, if a base station having one transmission antennatransmits a signal to a terminal having one reception antenna, theterminal should determine energy per symbol that can be received throughthe downlink and the amount of interference to be simultaneouslyreceived in a section in which the corresponding symbol is receivedusing the reference signal received from the base station, and shoulddetermine Es/Io (energy per symbol to interference power ratio). Thedetermined Es/Io is converted into a data transmission speed or a valuecorresponding to the data transmission speed, and is reported to thebase station in the form of a channel quality indicator (CQI) to enablethe base station to determine at what data transmission speed the basestation is to perform data transmission to the terminal in the downlink.

In the LTE-A system, the terminal feeds information on the channel stateof the downlink back to the base station so that the feedbackinformation can be used for downlink scheduling of the base station. Forexample, the terminal measures the reference signal that the basestation transmits to the downlink, and feeds information extracted basedon the reference signal back to the base station in the form defined inthe LTE/LTE-A standards. In the LTE/LTE-A, information that the terminalfeeds back to the base station is briefly classified into three kinds asfollows.

-   -   Rank indicator (RI): The number spatial layers that the terminal        can receive in the current channel state.    -   Precoding matrix indicator (PMI): an indicator of a precoding        matrix to which the terminal prefers in the current channel        state.    -   CQI: The maximum data rate at which the terminal can receive        data in the current channel state. The CQI may be replaced by an        SINR that can be used similarly to the maximum data rate,        maximum error correction code rate and modulation method, and        data efficiency per frequency.

The RI, PMI, and CQI have meanings in association with one another. Asan example, the precoding matrix supported in the LTE/LTE-A isdifferently defined by ranks. Accordingly, although the PMI value whenRI has a value of “1” and the PMI value when RI has a value of “2” areequal to each other, they are differently interpreted. Further, it isassumed that the rank value and the PMI value that the terminal reportedto the base station has been applied to the base station even in thecase where the terminal determines the CQI. For example, if the rank isRI_X and the precoding is PMI_Y in the case where the terminal hasreported RI_X, PMI_Y, and CQI_Z to the base station, it indicates thatthe terminal can receive the data rate corresponding to the CQI_Z. Asdescribed above, the terminal assumes in what transmission method theterminal performs transmission to the base station when calculating theCQI, and thus, it can obtain an optimum performance when performingactual transmission in the corresponding transmission method.

In the case of a base station that possesses a massive antenna toperform the channel information generation and report, it is necessaryfor the base station to configure reference signal resources formeasuring channels of 8 or more antennas to transmit the referencesignal resources to the terminal. As illustrated in FIG. 2, although anavailable CSI-RS resource can use maximally 48 REs, It is currentlypossible to configure up to 8 CSI-RSs for one CSI process. Accordingly,there is a need for a new CSI-RS configuration method to support anFD-MIMO system that can operate based on 8 or more CSI-RS ports.

As an example, in the LTE/LTE-A release 13, 1, 2, 4, 8, 12, or 16 CSI-RSports may be configured in one CSI process. Specifically, {1, 2, 4,8}-port CSI-RS follow the existing mapping rule, 12-port CSI-RS isconfigured as an aggregation of three 4-port CSI-RS patterns, and16-port CSI-RS is configured as an aggregation of two 8-port CSI-RSpatterns.

Further, in the LTE/LTE-A release 13, CDM-2 or CDM-4 is supported usingan orthogonal cover code (OCC) of length 2 or 4 with respect to12-116-port CSI-RSs. The above explanation of FIG. 3 refers to CSI-RSpower boosting based on CDM-2, and according to the above explanation,maximally 9 dB power boosting is necessary in comparison to the PDSCHfor full power utilization for the 12-/16-port CSI-RSs based on CDM-2.This indicates that high-performance hardware is necessary in comparisonto the existing one for the full power utilization during operation ofthe 12-/16-port CSI-RSs based on CDM-2. In the release 13, inconsideration of this, the 12-/16-port CSI-RSs based on CDM-4 have beenintroduced, and in this case, the full power utilization becomespossible through the existing 6 dB power boosting.

Currently, with the increase of dynamic precoding demands in thevertical direction, lively discussions have been developed on FD-MIMOincluding uniform planar array (UPA) antenna ports. As described above,the number of CSI-RS ports that can be currently configured in one CSIprocess is limited to {(1 or 2), 4, 8, 12, 16}. Accordingly, in order tosupport an FD-MIMO system having various two dimensional (2D) antennaarray shape, there is a need for a method for configuring CSI-RSsincluding various numbers of antenna ports, such as {18, 20, 22, 24, 26,28, 30, 32}.

The present disclosure has been made to solve the above problem, andprovides a method and an apparatus for generating CSI in order toperform effective data transmission/reception and sharing the generatedCSI in an LTE-A based FD-MIMO system. Specifically, in order to performhigh-efficiency data transmission/reception in an FD-MIMO systemaccording to an embodiment of the present disclosure, a method and anapparatus are provided, in which a base station notifies a terminal ofconfiguration information for a plurality of CSI-RSs, and the terminalgenerates feedback information in accordance with the configurationinformation.

As described above, the FD-MIMO base station should configure andtransmit to the terminal reference signal resources for measuringchannels for 8 or more antennas, and in this case, the number ofreference signals may differ in accordance with the base station antennaconfiguration and measurement types. As an example, in the LTE/LTE-Arelease 13, it is possible to configure {1, 2, 4, 8, 12, 16}-portCSI-RSs on the assumption of the full port mapping. Here, the full portmapping indicates that all transceiver units (TXRUs) have dedicatedCSI-RS ports for channel estimation.

On the other hand, after LTE/LTE-A release 14 as described above, thereis a high possibility that 16 or more TXRUs are introduced. Further,supportable antenna array shapes will be greatly increased in comparisonto the release 14. This indicates that various numbers of TXRUs shouldbe supported in the LTE/LTE-A release 14.

Table 1 below is an available 2D antenna array structure list. In Table1, {18, 20, 22, 24, 26, 28, 30, 32}-port CSI-RSs have been considered,and considering that two different polarization antennas may exist inthe same location in a polarization antenna structure, {9, 10, 11, 12,13, 14, 15, 16} numbered different AP locations may be considered. Onthe other hand, a 2D rectangular or square antenna array shape may bepresented by the number N₁ of different AP locations in the firstdimension (in vertical or horizontal direction) and the number N₂ ofdifferent AP locations in the second dimension (in horizontal orvertical direction), and possible aggregations in the respective portnumbers are (N₁, N₂) of Table 1. Table 1 indicates that various antennaarray shapes may exist in accordance with the number of CSI-RS ports.

TABLE 1 Number of Number of Available 2D antenna array Impact onaggregated aggregated CSI- geometry, (N₁, N₂) 2D RS and CSI-RS RS portsper (1D configurations were feedback ports polarization omitted) design18 9 (3, 3) — — — Low 20 10 (2, 5) (5, 2) — — Med 22 11 — — — — — 24 12(2, 6) (3, 4) (4, 3) (6, 2) High 26 13 — — — — — 28 14 (2, 7) (7, 2) — —Med 30 15 (3, 5) (5, 3) — — Med 32 16 (2, 8) (4, 4) (8, 2) — High

As described above, in order to support 16 or more CSI-RS ports, it isnecessary to consider various items as follows.

-   -   A method for configuring CSI-RSs including a large number of        ports suitable for various 2D antenna array shapes including a        cross polarization structure and channel states    -   A method for reducing CSI-RS resource overhead due to a large        number of CSI-RS ports

In embodiments described hereinafter, a method for configuring aplurality of CSI-RS ports in consideration of one or more of theabove-described items will be described. Although embodiments aredecomposedly described for convenience in explanation, they are notindependent from each other, and two or more embodiments may beaggregated to be applied.

In an embodiment of the present disclosure, a time-frequency resourceregion including the whole or a part of configured CSI-RS ports isexpressed as a CSI-RS PRB pair or a CSI-RS PRB, and it can be expressedas several similar meanings, such as CSI-RS subframe, CSI-RS subband,and CSI-RS bandwidth.

Further, in an embodiment of the present disclosure, althoughrestriction so as to generate the CSI using a part of the RSstransmitted to the whole bands or the whole RS subframes is expressed asfrequency comb/time comb transmission, it can be named as similarexpressions, such as frequency/time measurement restriction andfrequency/time measurement window.

First Embodiment

One method to reduce a CSI-RS resource overhead is to lower the densityof CSI-RS REs. For this, it can be configured that the CSI-RStransmission resource is decomposed into several groups includingdifferent time or frequency resources and respective CSI-RS ports aretransmitted from only parts of the groups.

In the standards up to the LTE/LTE-A release 13, CSI-RSs are transmittedover the whole band, and PRBs from which the CSI-RSs are transmitted aredetermined to include the CSI-RS REs for all the CSI-RSs. For example,the density of the CSI-RS RE is 1RE/port/PRB. On the other hand, methodsas illustrated in FIGS. 4A and 4B can be hereafter used in order tosupport 16 or more CSI-RS ports, in order to provide UE-specificbeamformed CSI-RSs to a plurality of terminals, or in order to providemany kinds of cell-specific beamformed CSI-RSs.

As an example, the whole CSI-RS ports may be decomposed into two or moresubgroups by a certain basis. The CSI-RS subgroup may be explicitlyreported to the terminal by higher layer signaling or physical layersignaling, or may be explicitly/suggestively reported to the terminal byone or more CSI-RS resource configuration lists or one or more CSI-RSconfiguration lists.

The decomposed CSI-RS ports may be transmitted from different resourcesby subgroups. FIGS. 4A and 4B are diagrams illustrating an example ofCSI-RS subgroup mapping on time axis or frequency axis. For example, itis assumed that the whole CSI-RS ports are decomposed into twosubgroups, that is, group A 400 and group B 410. In this case, as shownin FIG. 4A, the CSI-RSs belonging to group A and group B are transmittedover the whole frequency band, but may be decomposed through differenttime resources (subframes) to be transmitted. Further, as shown in FIG.4B, the CSI-RSs are transmitted from all CSI-RS subframes (i.e.,transmitted over the whole time axis), but may be decomposed throughdifferent PRBs to be transmitted. FIGS. 4A and 4B are merely exemplary,and it is not necessary that distributions of time or frequencyresources are always equal to each other by CSI-RS port subgroups asshown in FIGS. 4A and 4B. Further, it is apparently possible to allocatea larger number of resources to important subgroups.

It is also possible that the above example is functionally equallyanalyzed as follows. The whole CSI-RS REs may be decomposed into two ormore subgroups by a certain basis. The CSI-RS RE subgroup may beexplicitly reported to the terminal by higher layer signaling orphysical layer signaling, or may be explicitly/suggestively reported tothe terminal by one or more CSI-RS resource configuration lists or oneor more CSI-RS resource configuration lists. The CSI-RS ports may betransmitted from at least one of the decomposed CSI-RS RE subgroups. Forexample, it is assumed that the whole CSI-RS REs are decomposed into twosubgroups, that is, group A and group B. In this case, as shown in FIG.4A, the CSI-RS ports transmitted from the subgroups A and B aretransmitted over the whole frequency band, but may be decomposed throughdifferent time resources (subframes) to be transmitted. Further, asshown in FIG. 4B, the CSI-RS ports are transmitted from all CSI-RSsubframes (i.e., transmitted over the whole time axis), but may bedecomposed through different PRBs to be transmitted. FIGS. 4A and 4B aremerely exemplary, and it is not necessary that distributions of time orfrequency resources are always equal to each other by CSI-RS REsubgroups as shown in FIGS. 4A and 4B. Further, it is apparentlypossible to allocate a larger number of resources to importantsubgroups.

In the present disclosure as described above, the CSI-RS subgroup may beanalyzed as a port subgroup or RE subgroup, and one method may beswitched to the other method through a similar way. Accordingly, theCSI-RS subgroup may be commonly called as “subgroup” or “CSI-RSsubgroup”.

FIGS. 4A and 4B are diagrams illustrating CSI-RS subgroup mapping on atime axis or frequency axis according to various embodiments of thepresent disclosure.

Referring to FIGS. 4A and 4B, such subgroup configuration can make RSintervals uniform, and thus terminal implementation can be simplified.However, it is not necessary to limit the actual subgroup configurationto the comb type, and it is also possible to engage transmission in aspecific band for each subgroup, such as localized transmission.

As an example to configure the CSI-RS subgroups (or component (orreference) CSI-RS resources, it is possible to tie the CSI-RS ports inthe first or second direction (vertical or horizontal direction) or perpolarization. A CSI-RS port index may be configured by a base station toa terminal using signaling, and the signaling may include both higherlayer signaling and physical layer signaling. The CSI-RS subgroupconfiguration method can be applied in various manners in accordancewith the antenna array shape or channel state. For example, if thefirst-direction array size N₁ is smaller than the second-direction arraysize N₂, the system performance may be more greatly affected by thesecond-direction component, or in a situation in which the antenna arraysize is very large and several UEs discriminate channels of several UEsthrough a direction component other than a co-phasing component, it willbe important to accurately measure the direction component throughsubgroup configuration per polarization.

FIGS. 5A and 5B are diagrams illustrating CSI-RS subgroup generation forfull port mapping and partial port mapping in an environment in which 20TXRUs exist according to various embodiments of the present disclosure.

Referring to FIGS. 5A and 5B, 500 and 510 denote first and second CSI-RSsubgroups. Further, a solid line indicates TXRUs to which CSI-RS portsare allocated in the corresponding CSI-RS subgroups, and a dotted lineindicates TXRUs to which CSI-RS ports are not allocated in thecorresponding CSI-RS subgroup.

In FIG. 5A, full port mapping exemplifies CSI-RS subgroup generation perpolarization. According to the full port mapping of FIGS. 5A, 5B, and5C, 10 CSI-RS ports corresponding to −45°-pol AP may be allocated to thefirst CSI-RS subgroup 500, and 10 CSI-RS ports corresponding to +45°-polAP may be allocated to the second CSI-RS subgroup 510. Full portmappings of FIGS. 5B and 5C exemplifies CSI-RS subgroup generation perdirection. According to the full port mapping of FIG. 5B, the respectiveCSI-RS subgroups may include the same number of vertical orhorizontal-direction CSI-RS ports. In particular, according to full portmapping of FIG. 5C, the respective CSI-RS subgroups may include severalkinds of vertical or horizontal-direction CSI-RS ports, and eachsubgroup may include different numbers of CSI-RS ports.

In FIG. 5B, the partial port mapping indicates that partial TXRUs havededicated CSI-RS ports for channel estimation, but other partial TXRUsdo not have corresponding CSI-RS ports. The partial port mapping of FIG.5A exemplifies CSI-RS subgroup generation per direction. In thisexample, the first CSI-RS subgroup includes 10 horizontal-directionCSI-RS ports, and the second CSI-RS subgroup includes 4vertical-direction CAI-RS ports. In this case, partial TXRUs may not beallocated with the CSI-RS ports. The partial port mapping of FIG. 5Bexemplifies CSI-RS subgroup generation per polarization, and in thiscase, −45° or +45°-pol APs are all allocated to the first CSI-RSsubgroup without subsampling. Through this, the terminal can properlyestimate co-phasing information of the channel.

CSI-RS overhead reduction through partial port mapping may be similarlyperformed even without CSI-RS subgroup configurations.

FIGS. 6A and 6B are diagrams illustrating partial port mapping beingperformed without CSI-RS subgroup configurations according to variousembodiments of the present disclosure.

Referring to FIG. 6A, the partial port mapping of FIG. 5A may beperformed within one CSI-RS resource. As another example, FIG. 6B showsthat the partial port mapping of FIG. 5B may be performed within oneCSI-RS resource. FIG. 6B illustrates a situation in which only twoCSI-RS ports are configured for +45°-pol AP.

The examples in Table 1 and FIGS. 5A, 5B, and 5C as described above meanthat the number of CSI-RS subgroups or components (CSI-RS resources) andthe number of CSI-RS ports included in each CSI-RS subgroup may differdepending on the situation. Accordingly, in order to support this, thereis a need for a CSI-RS resource decomposition method with a flexiblestructure. For example, the base station may differently configure aCSI-RS transmission period and whether to transmit (or configure) CSI-RSsubbands by CSI-RS subgroups. Further, the different CSI-RS subgroupsmay be including different numbers of CSI-RS ports.

As one example to perform this, comb configuration (time comb (comb_(T))and/or frequency comb (comb_(F)) may be defined on the time or frequencyaxis. The base station may respectively or simultaneously configure thecomb_(T) or comb_(F), and may report to the terminal from whattime/frequency resources the respective CSI-RS subgroups are to betransmitted.

FIG. 7 is a diagram illustrating CSI-RS configurations by comb_(T) orcomb_(F), according to an embodiment of the present disclosure.

Referring to FIG. 7, the base station may configure a time comb tocomb_(T)∈{X, 0, 1} with respect to the time axis. Here, X indicates thatthe time comb is not applied, i.e., that the corresponding CSI-RSsubgroup is transmitted from all CSI-RS subframes. Here, “0” indicatesthat the CSI-RS subgroups are transmitted from odd CSI-RS subframes, and“1” indicates that CSI-RS subgroups are transmitted from even CSI-RSsubframes. The meanings of X, 0, and 1 are examples of time combconfiguration, and it is apparent that they may be determined withvarious meanings when they are actually applied.

Referring to FIG. 7, it is assumed that the CSI-RS transmission periodis set to 5 ms. In an example of FIG. 7, it can be seen that the timecomb of CSI-RS subgroup A 700 is configured to comb_(T)=X, and CSI-RSports belonging to subgroup A are transmitted from all the CSI-RSsubgroups having 5 ms period. On the other hand, time combs of CSI-RSsubframe B 710 and CSI-RS subgroup C 720 are set to “0” and “1,” and itcan be seen that CSI-RS ports belonging to subgroup B are transmittedfor each 10 ms from odd CSI-RS subframes, and CSI-RS ports belonging tosubgroup C are transmitted for each 10 ms from even CSI-RS subframes.

Even with respect to frequency combs, it is possible to apply similarconfiguration to the time comb. In an example of FIG. 7, the basestation may configure a frequency comb to comb_(F)∈{X, 0, 1} withrespect to the frequency axis. Here, X indicates that the frequency combis not applied, i.e., that the corresponding CSI-RS subgroup istransmitted from all PRBs. Here, “0” indicates that the CSI-RS subgroupsare transmitted from odd PRBs, and “1” indicates that CSI-RS subgroupsare transmitted from even PRBs. The meanings of X, 0, and 1 are examplesof frequency comb configuration, and it is apparent that they may bedetermined with various meanings (e.g., in the unit of several PRBgroups) when they are actually applied.

In an example of FIG. 7, it can be seen that the frequency comb ofCSI-RS subgroup A 700 is configured to comb_(F)=0, and CSI-RS portsbelonging to subgroup A are transmitted from odd PRBs. On the otherhand, frequency combs of CSI-RS subframe B 710 and CSI-RS subgroup C 720are set to “1,” and CSI-RS ports belonging to subgroups B and C aretransmitted from even PRBs.

As another example of CSI-RE subgroup configuration, there is a methodfor explicitly individually configure CSI-RS resources used to transmitrespective CSI-RS subgroups. In this example, CSI-RS configurationinformation, such as CSI-RS transmission period, transmission offset,CSI-RS resource index, a list of indexes, or information on the CSI-RStransmission band, may be separately configured by CSI-RS subgroups.Further, the base station may report to the terminal what CSI-RS port isincluded in the CSI-RS subgroups through higher layer signaling orphysical layer signaling.

Referring to Tables 2-1 to 2-4 below, a CSI process includes at leastone CSI-RS resource configuration, and each CSI-RS resourceconfiguration can be configured as one of a non-precoded CSI-RS andbeamformed CSI-RSs.

First, the CSI-RS resource configuration that is configured asnon-precoded CSI-RSs includes at least one CSI-RS configuration, andeach CSI-RS configuration includes antennaPortsCount-numbered CSI-RSREs. For example, if one non-precoded CSI-RS has N CSI-RSconfigurations, and is configured to antennaPortsCount=P, the totalnumber of CSI-RS REs that are used for the non-precoded CSI-RSs becomesNP. In the case of the non-precoded CSI-RSs, the unit of the CSI-RSsubgroup may be the CSI-RS resource configuration or CSI-RSconfiguration.

If the unit of the CSI-RS subgroup is the CSI-RS resource configuration,this indicates that the same subgroup configuration is applied to allCSI-RS configurations constituting one CSI-RS resource configuration.Table 2-1 below relates to CSI-RS comb type configuration by CSI-processinformation elements. If subgroups are configured in time/frequency combtype, TM10 terminal that uses a CSI process may be added with resourceradio control (RRC) parameters, such as (2-1-00) or (2-1-01) in Table2-1. In Table 2-1, (2-1-00) performs signaling of a subgroup shape in afrequency domain, and (2-1-01) performs signaling of a subgroup shape ina time domain. In this case, X and Y mean the number of subgroup shapesin the frequency/time domains. For example, if two kinds of comb typesare supported in the frequency domain and no subgroup exists in the timedomain, X becomes “1,” and (2-1-00) may not be configured or defined.Similarly to this, it is also possible to use (2-1-00) or (2-1-01) forthe purpose of signaling processing granularity in the frequency/timedomain. For example, if (2-1-00) has a value of “1,” it may be analyzedthat frequency measurement restriction is turned on, and independentchannel estimation by PRBs should be performed, or channel estimationshould be performed by certain PRB groups. As another example, if(2-1-00) has a value of “4,” it may be analyzed that frequencymeasurement restriction is turned on, and channel estimation may beperformed through grouping of four PRBs.

Table 2-2 relates to CSI-RS comb type configuration by CSI-RS comb typeconfiguration by CSI-RS-config information elements. In the case of TM9terminal, the CSI process is not configured, and thus it is possible toperform signaling of the frequency or time domain subgroup shapes, suchas (2-2-00) or (2-2-01). Since the detailed explanation is similar tothat of the TM10 terminal, it will be omitted.

As another example of subgroup configuration, if the unit of the CSI-RSsubgroup becomes CSI-RS configuration, this indicates that independentsubgroup configuration is applied to individual CSI-RS configurations.Of course, even in this case, it is apparent that the same subgroupshape can be applied to all CSI-RS configurations in accordance withhigher layer configuration. Table 2-3 relates to CSI-RS comb typeconfiguration by CSI-RS-ConfigNZP information elements. In Table 2-1below, one CSI process may be configured to nonPrecoded-r13 orbeamformed-r13 of Table 2-2 below by RRC parameter eMIMO-Type-r13. Ifthe one CSI process is configured to non-precoded CSI-RSs, the terminalmay configure one CSI-RS resource through aggregation of one ofresourceConfig-r10 in Table 2-2 and resourceConfig-r11 of table 2-3 withnzp-resourceConfigList-r13 in Table 2-3. In this example, in order fordifferent subgroup designations by resourceConfig to become possible,RRC parameters, such as (2-2-00), (2-2-01), (2-2-02), (2-2-03),(2-2-04), (2-2-10), (2-2-11), (2-2-16), (2-2-17) in Table 2-2, may bedefined. Here, (2-2-16) and (2-2-17) respectively perform signaling ofsubgroup shapes in the frequency/time domains, and X and Y indicates thenumbers of subgroup shapes in the respective domains. The detailedexplanation thereof may refer to the above-described examples. It isalso possible that the signaling presents the same meaning asinformation elements related to respective CSI-RS configurations(resourceConfig), such as (2-2-02), (2-2-03), and (2-2-04), through(2-2-10) or (2-2-11) that are separate lower layer information elements.It is also possible that (2-2-04) is defined in the same manner as(2-3-02) in Table 2-3.

Second, the terminal may be configured to receive the beamformedCSI-RSs. In the case of the beamformed CSI-RS, it is possible toconfigure at least one CSI-RS resource configuration in one CSI process.In this case, respective CSI-RS resource configurations include oneCSI-RS configuration value. Specifically, the terminal may receivesignaling of minimally one to maximally 8 CSI-RS configurations(resourceConfig) through one of resourceConfig-r10 in Table 202 andresourceConfig-r11 in Table 2-3 and csi-RS-ConfigNZPIdListExt in Table2-2. In this example, in order for different subgroup designations byresourceConfigs to become possible, RRC parameters, such as (2-2-00),(2-2-01), (2-2-02), (2-2-03), (2-2-06), (2-2-10), (2-2-11), (2-2-16),and (2-2-17) in Table 2-2, may be defined. In the case of beamformedCSI-RSs, one subgroup configuration by respective CSI-RS resourceconfigurations is possible, and CSI-RS ports included in the same CSI-RSresource configuration are not included in different subgroups. Sincethe relationship between the respective parameters is similar to that ofnon-precoded CSI-RSs, the detailed explanation thereof will be omitted.

Although the above-described examples have been described based onnon-zero power (NZP) CSI-RS configurations, it is possible to apply thesame subgroups as the NZP CSI-RS even to zero power (ZP) CSI-RS andCSI-IM. The ZP CSI-RS and the CSI-IM may be used for the purpose oflowering inter-cell interference by the CSI-RS or of measuring theinterference using the CSI-RS resources. Accordingly, if the CSI-RS istransmitted in accordance with the subgroup configuration, it isnecessary for suitable subgroup configuration to be applied to the ZPCSI-RS and the CSI-IM to match the same. Table 2-4 relates to ZP CSI-RScomb type configurations by CSI-RS-ConfigZP information elements. Forthis, RRC parameters may be defined, such as (2-2-05), (2-2-07),(2-2-08), (2-2-09), (2-2-12), (2-2-13), (2-2-14), and (2-2-15) in Table2-2, and (2-4-00), (2-4-01), (2-4-02), (2-4-03), and (2-4-05) in Table2-4. Since the relationship between the respective parameters is similarto that of NZP CSI-RSs, the detailed explanation thereof will beomitted. In this case, (2-4-00) and (2-4-01) may not be simultaneouslyconfigured or defined. Here, (2-4-00) has the feature capable ofconfiguring different subgroups by 4-port CSI-RSs designated by therespective ZP CSI-RS resourceConfigList, and (2-4-01) configures thesame subgroup in all 4-port CSI-RSs designated by 16-bit ZP CSI-RSresourceConfigList bit map.

TABLE 2-1 -- ASN1START CSI-Process-r11 ::= SEQUENCE { csi-ProcessId-r11CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11,csi-IM-ConfigId-r11 CSI-IM-ConfigId-r11, p-C-AndCBSRList-r11 SEQUENCE(SIZE (1..2)) OF P-C-AndCBSR-r11, cqi-ReportBothProc-r11CQI-ReportBothProc-r11 cqi-ReportPeriodicProcId-r11 INTEGER(0..maxCQI-ProcExt-r11) cqi-ReportAperiodicProc-r11CQI-ReportAperiodicProc-r11 ..., < Portions of which explanation isunnecessary are omitted > [[ cqi-ReportAperiodicProc-v1310 CHOICE {release NULL, setup CQI- ReportAperiodicProc-v1310 }cqi-ReportAperiodicProc2-v1310 CHOICE { release NULL, setup CQI-ReportAperiodicProc-v1310 } eMIMO-Type-r13 CSI-RS- ConfigEMIMO-r13 ]] [[transmissionComb-Freq INTEGER {0..X} → (2-1-00) transmissionComb-TimeINTEGER {0..Y} → (2-1-01) ]] } < Portions of which explanation isunnecessary are omitted > -- ASN1STOP

TABLE 2-2 -- ASN1START CSI-RS-Config-r10 ::= SEQUENCE { csi-RS-r10CHOICE { release NULL, setup SEQUENCE { antennaPortsCount-r10 ENUMERATED{an1, an2, an4, an8}, resourceConfig-r10 INTEGER (0..31),subframeConfig-r10 INTEGER (0..154), p-C-r10 INTEGER (−8..15) } }zeroTxPowerCSI-RS-r10 ZeroTxPowerCSI-RS-Conf-r12 [[transmissionComb-Freq INTEGER {0..X} → (2-2-00) transmissionComb-TimeINTEGER {0..Y} → (2-2-01) ]] } CSI-RS-Config-v1250 ::= SEQUENCE {zeroTxPowerCSI-RS2-r12 ZeroTxPowerCSI-RS-Conf-r12ds-ZeroTxPowerCSI-RS-r12 CHOICE { release NULL, setup SEQUENCE {zeroTxPowerCSI-RS-List-r12 SEQUENCE (SIZE (1..maxDS-ZTP-CSI-RS-r12)) OFZeroTxPowerCSI-RS-r12 } } } CSI-RS-Config-v1310 ::= SEQUENCE {eMIMO-Type-r13 CSI-RS-ConfigEMIMO-r13 [[ transmissionComb-Freq INTEGER{0..X} → (2-2-02) transmissionComb-Time INTEGER {0..Y} → (2-2-03) ]] }CSI-RS-ConfigEMIMO-r13 ::= CHOICE { release NULL, setup CHOICE {nonPrecoded-r13 CSI-RS-ConfigNonPrecoded- r13, beamformed-r13CSI-RS-ConfigBeamformed- r13 } } CSI-RS-ConfigNonPrecoded-r13 ::=SEQUENCE { p-C-AndCBSRList-r13 P-C-AndCBSR- PerResourceConfig-r13codebookConfigN1-r13 ENUMERATED  {n1, n2, n3, n4, n8},codebookConfigN2-r13 ENUMERATED  {n1, n2, n3, n4, n8},codebookOverSamplingRateConfig-O1-r13 ENUMERATED {n4, n8}codebookOverSamplingRateConfig-O2-r13 ENUMERATED {n4,n8}codebookConfig-r13 INTEGER (1..4), csi-IM-ConfigIdList-r13 SEQUENCE(SIZE (1..2)) OF CSI-IM-ConfigId-r13 csi-RS-ConfigNZP-EMIMO-r13CSI-RS-ConfigNZP- EMIMO-r13 [[ NZP-TransmissionCombList SEQUENCE (SIZE(1..2)) OF NZP-TransmissionComb → (2-2-04) IM-TransmissionCombListSEQUENCE (SIZE (1..2))  OF  IM-TransmissionComb → (2-2-05) ]] }CSI-RS-ConfigBeamformed-r13 ::= SEQUENCE { csi-RS-ConfigNZPIdListExt-r13SEQUENCE (SIZE (1..7)) OF CSI-RS-ConfigNZPId-r13 csi-IM-ConfigIdList-r13SEQUENCE (SIZE (1..8)) OF CSI-IM-ConfigId-r13p-C-AndCBSR-PerResourceConfigList-r13 SEQUENCE (SIZE (1..8)) OFP-C-AndCBSR-PerResourceConfig-r13 ace-For4Tx-PerResourceConfigList-r13SEQUENCE (SIZE (1.7)) OF BOOLEANalternativeCodebookEnabledBeamformed-r13 ENUMERATED {true}channelMeasRestriction-r13 ENUMERATED  {on} [[ NZP-TransmissionCombListSEQUENCE (SIZE (1..7)) OF NZP-TransmissionComb → (2-2-06)IM-TransmissionCombList SEQUENCE (SIZE (1..8))  OF  IM-TransmissionComb→ (2-2-07) ]] } ZeroTxPowerCSI-RS-Conf-r12 ::= CHOICE { release NULL,setup ZeroTxPowerCSI-RS- r12 } ZeroTxPowerCSI-RS-r12 ::= SEQUENCE {zeroTxPowerResourceConfigList-r12 BIT STRING (SIZE (16)),zeroTxPowerSubframeConfig-r12 INTEGER (0..154) [[ZP-TransmissionCombList SEQUENCE (SIZE (1..16)) OF ZP-TransmissionComb →(2-2-08) ZP-TransmissionComb ZM-TransmissionComb → (2-2-09) ]] }NZP-TransmissionComb ::= SEQUENCE { transmissionComb-FreqTransmissionComb-Freq, → (2-2-10) transmissionComb-TimeTransmissionComb-Time, → (2-2-11) ... } ZP-TransmissionComb ::= SEQUENCE{ transmissionComb-Freq TransmissionComb-Freq, → (2-2-12)transmissionComb-Time TransmissionComb-Time, → (2-2-13) ... }IM-TransmissionComb ::= SEQUENCE { transmissionComb-FreqTransmissionComb-Freq, → (2-2-14) transmissionComb-TimeTransmissionComb-Time, → (2-2-15) ... } TransmissionComb-Freq ::=INTEGER {0..X} → (2-2-16) TransmissionComb-Time ::= NTEGER {0..Y} →(2-2-17) -- ASN1STOP

TABLE 2-3 -- ASN1START CSI-RS-ConfigNZP-r11 ::= SEQUENCE {csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11, antennaPortsCount-r11ENUMERATED {an1, an2, an4, an8}, resourceConfig-r11 INTEGER (0..31),subframeConfig-r11 INTEGER (0..154), scramblingIdentity-r11 INTEGER(0..503), qcl-CRS-Info-r11 SEQUENCE { qcl-ScramblingIdentity-r11 INTEGER(0..503), crs-PortsCount-r11 ENUMERATED {n1, n2, n4, spare1},mbsfn-SubframeConfigList-r11 CHOICE { release NULL, setup SEQUENCE {subframeConfigList MBSFN- SubframeConfigList } } } ..., [[csi-RS-ConfigNZPId-v1310 CSI-RS-ConfigNZPId-v1310 ]] [[transmissionComb-Freq INTEGER {0..X} → (2-3-00) transmissionComb-TimeINTEGER {0..Y} → (2-3-01) ]] } CSI-RS-ConfigNZP-EMIMO-r13 CHOICE {release NULL, setup SEQUENCE { nzp-resourceConfigList-r13 SEQUENCE (SIZE(1..2)) OF NZP-ResourceConfig-r13, cdmType-r13 ENUMERATED {cdm2, cdm4}[[ NZP-TransmissionCombList SEQUENCE (SIZE (1..2)) OFNZP-TransmissionComb → (2-3-02) ]] } } NZP-ResourceConfig-r13 ::=SEQUENCE { resourceConfig-r13 ResourceConfig-r13, ... }ResourceConfig-r13 INTEGER (0..31) NZP-TransmissionComb ::= SEQUENCE {transmissionComb-Freq TransmissionComb-Freq, → (2-3-03)transmissionComb-Time TransmissionComb-Time, → (2-3-04) ... }TransmissionComb-Freq ::= INTEGER {0..X} → (2-3-05)TransmissionComb-Time ::= INTEGER {0..Y} → (2-3-06) -- ASN1STOP

TABLE 2-4 -- ASN1START CSI-RS-ConfigZP-r11 ::= SEQUENCE { csi-RS-ConfigZPId-r11  CSI-RS-ConfigZPId-r11,  resourceConfigList-r11 BIT STRING (SIZE (16)),  subframeConfig-r11  INTEGER (0..154),  [[ZP-TransmissionCombList    SEQUENCE (SIZE (1..16)) OFZP-TransmissionComb  → (2-4-00)   ZP-TransmissionComb    ZM-TransmissionComb     → (2-4-01)  ]]  ... } ZP-TransmissionComb::= SEQUENCE {  transmissionComb-Freq    TransmissionComb-Freq,   →(2-4-02)  transmissionComb-Time    TransmissionComb-Time,   → (2-4-03) ... } TransmissionComb-Freq ::=   INTEGER {0..X}    → (2-4-04)TransmissionComb-Time ::=   INTEGER {0..Y}    → (2-4-05) -- ASN1STOP

In the above-described embodiment, the RRC parameters are defined on theassumption that comb type CSI-RS transmission is supported in thefrequency and time domains, but actual application is not necessarilylimited thereto. For example, it is also possible to support onlysubgroup configurations in the frequency domain, the subgroup shape maybe defined as various other items, such as frequency domain measurementrestriction. In this case, the RRC parameters can be analyzed anddefined with other proper expressions.

FIG. 8 is a diagram illustrating CSI-RS resources having low overheadthat may be configured to a terminal according to an embodiment of thepresent disclosure.

Referring to FIG. 8, it is assumed that overhead of a frequency domainis reduced, and it is possible that the respective CSI-RS ports aretransmitted from one of even PRB group (or comb type A) and odd PRBgroup (or comb type B). Although FIG. 8 illustrates a case where 24CSI-RS ports are transmitted for convenience, the number of CSI-RS portsis not limited thereto, but can be extended to various cases, such as20, 28, 32, and 64.

As an example, as 800 of FIG. 8, all CSI-RS ports may be configured tobe transmitted from the odd PRB group (or even PRB group). In this case,since the CSI-RS ports exist in one RB, they are strengthened infrequency/time selectivity of the channel, and have advantageouscharacteristics to estimation of channel direction information for PMIdetermination. In contrast, unlike the CSI-RSs up to Release 13, theCSI-RS ports are not transmitted for each PRB, and thus greaterinfluence may be exerted on the existing terminals from the viewpoint ofPDSCH rate matching.

As another example, as indicated as 801, 802, 803, and 804 in FIG. 8, itmay be configured that partial CSI-RS ports 801 and 802 are transmittedfrom an odd PRB group 810, and the remaining CSI-RS ports 803 and 804are transmitted from an even PRB group 820. In this case, since allCSI-RS ports do not exist in one RB, they may have somewhat sensitivecharacteristics in the frequency/time selectivity of the channel, butsince the CSI-RS ports are transmitted for each PRB, the influenceexerted on the existing terminals can be reduced.

Second Embodiment

Proposed second embodiment will be described with reference to FIGS. 9,10, 11, 12, 13, 14, 15, 16, and 17.

FIG. 9 is a diagram illustrating CSI-RS port sharing according to anembodiment of the present disclosure.

Referring to FIG. 9, as an example of enhanced FD (eFD)-MIMO or newradio (NR) MIMO base station, such as 900 of FIG. 9, a base stationhaving an antenna structure of (n1=2, N2=8, P=2) may be assumed. Here,n1 denotes the number of antenna ports in a vertical direction of a basestation antenna array, N2 denotes the number of antenna ports in ahorizontal direction of the base station antenna array, and P=2indicates that a cross-pol antenna is used. In such an environment, thetotal number of antenna ports becomes N1*N2*P=32. N1, N2, and P can beextended to various numbers.

Hereafter, even if a base station such as 900 of FIG. 9 iscommercialized, there is a high probability that on a network, not onlynew terminals of release 14 or thereafter, such as 904, but alsoterminals of release 13 or heretofore, in which the antenna shape of 900is unable to be recognized as 905 and 906, have still been used. If thebase station intends to support the CSI-RSs of the existing terminals,such as 905 or 906, using independent resources, it uses about 3.3% ofthe resources in order to transmit 8-port CSI-RSs to the terminals, suchas 906, up to release 12, and uses about 6.7% of the resources in orderto transmit 16-port CSI-RSs to the release 13 terminals, such as 905.This indicates that the network may additionally bear maximally up to10% of the frequency/time resources to support the existing terminals.

In order to lighten such a burden, a method in which a smaller number ofCSI-RS port transmission is nested in a larger number of CSI-RS porttransmission may be considered. As an example, transmission of 8-portCSI-RSs 903 of FIG. 9 may be nested as a part of transmission of 16-portCSI-RSs 902 that is larger than the transmission of 8-port CSI-RSs, andthe transmission of 16-port CSI-RSs 902 may be nested as a part oftransmission of 32-port CSI-RSs 901 that is larger than the transmissionof 16-port CSI-RSs. This method can be efficiently used especially atthe time when 5G introduction is initiated or 4G terminal is almostwithdrawn.

FIG. 10 is a diagram illustrating a resource configuration for eachterminal for CSI-RS port sharing according to an embodiment of thepresent disclosure.

Referring to FIG. 10, it is assumed that the CSI-RS RE density for alarger number of CSI-RS ports is different from the CSI_RS RE densityfor a small number of CSI-RS ports through application of the firstembodiment as described above. As an example, a base station can receiveup to 32 CSI-RS ports. 32 CSI-RS ports in total, which corresponds to15th to 30th ports, may be configured to terminal A using four CSI-RSconfigurations 1010, 1020, 1030, and 1040, such as 1000 of FIG. 10. Inthis case, it is assumed that 8 ports configured through the firstCSI-RS configuration 1010 and 8 ports configured through the secondCSI-RS configuration 1020 are configured to be transmitted from an oddPRB group 1050, and 16 ports configured through the third and fourthCSI-RS configurations 1030 and 1040 are configured to be transmittedfrom an even PRB group 1060. The base station configures CSI-RS ports,such as 1001 of FIG. 10, to terminal B, and in this case, the basestation can transmit the CSI-RSs to the terminal B that can receive upto 16 CSI-RS ports using resources, such as frequency/time resourcesdesignated by four CSI-RS configurations for the terminal A.

In an example of FIG. 10, the base station may configure so thatresources designated by the first and third CSI-RS configurations 1010and 1030 for the terminal A and comb type indicators become equal toresources designated by the first CSI-RS configuration 1010 for theterminal B. Similarly, the base station may configure so that resourcesdesignated by the second and fourth CSI-RS configurations 1020 and 1040for the terminal A and the comb type indicators become equal toresources designated by the second CSI-RS configuration 1020 for theterminal B. Through the configuration as shown in FIG. 10, the basestation enables the existing terminals to aggregate two low-overheadCSI-RS ports to recognize the same as one CSI-RS port. This example willbe described with reference to FIGS. 12, 13, 14, and 15.

FIG. 11 is a diagram illustrating a CSI-RS resource configuration foreach terminal when CSI-RS is configured to a terminal after release 14with CSI-RS RE density of one RE/RB/port according to an embodiment ofthe present disclosure.

Referring to FIG. 11, it is assumed that an orthogonal code CDM-2 oflength 2 is configured to all terminals, and a base station has 32antenna ports expressed as 1100, 1101, 1102, and 1103. In order totransmit CSI-RSs for 32 antenna ports, the base station may configurefour component CSI-RS configurations of 1100, 1101, 1102, and 1103. Inthe LTE-A, a terminal up to release 12 can receive CDM-2 CSI-RS, and arelease 13 terminal can receive CDM-2 and CDM-4 CSI-RSs. Accordingly, inthe case of performing CSI-RS port sharing based on CDM-2, it isimportant to perform CSI-RS port sharing simultaneously with the release12 and release 13 terminals.

Since the release 12 terminal receives configuration of CSI-RS resourcesthrough a single CSI-RS configuration, CSI-RS port information forcross-pol antennas should be included in one CSI-RS configuration.Accordingly, in order to perform the CSI-RS port sharing with therelease 12 terminal, it is necessary that terminals of release 13 andthereafter include CSI-RS port information for the cross-pol antenna inone CSI-RS configuration.

As an example, referring to FIG. 11, the base station may allocate 8CSI-RS ports, such as 1104, to 8 cross-pol antenna ports adjacent in ahorizontal direction for terminals that can recognize maximally 8 CSI-RSports. In consideration of 8Tx code book, the port numbers of 8 portCSI-RSs should be first increased in the horizontal direction withrespect to +45°-pol (or −45°-pol) antennas, and then should be firstincreased in the horizontal direction with respect to −45°-pol (or+45°-pol) antennas with their polarity changed. Accordingly, it ispossible to use the port number, such as the component CSI-RSconfiguration 1100, as the CSI-RS port number for the CSI-RS resource1104.

Further, the base station may allocate 16 CSI-RS ports by configuring aplurality of CSI-RS configurations, such as (1105, 1106) or (1105,1107), to 16 cross-pol antenna ports adjacent in the horizontal orvertical direction for terminals that can recognize maximally 16 CSI-RSports. Here, (1105, 1106) are to configure 16-port CSI-RSs having anarray shape of (N1=1, N2=8, P=2), and (1105, 1107) are to configure16-port CSI-RSs having an array shape of (N1=2, N2=4, P=2). In the caseof the configuration, such as (1105, 1106), the terminal is unable toobtain channel information in the vertical direction, but it can obtainchannel information in more accurate horizontal direction, whereas inthe case of the configuration, such as (1105, 1107), the terminal canobtain channel information in both vertical and horizontal directions.

In order to perform port sharing with 8-port CSI-RS, the CSI-RS ports of1105 in FIG. 11 should be transmitted to the same antenna ports as thoseof the CSI-RS ports of 1104. Accordingly, both the antenna components(+45°-pol & −45°-pol) having two kinds of polarities should be includedeven in the CSI-RS configuration 1105, and for this, a port numberingrule as expressed in Mathematical expression 1 may be used.

$\begin{matrix}{\mspace{515mu}{{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 1}} \\{p = \left\{ \begin{matrix}{p^{\prime} + {\frac{N_{ports}^{CSI}}{2}\; i}} & {{{for}\mspace{14mu} p^{\prime}} \in \left\{ {15,\ldots\mspace{14mu},{15 + {N_{ports}^{CSI}/2} - 1}} \right\}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{2}\;\left( {i + N_{res}^{CSI} - 1} \right)}} & \begin{matrix}{{{for}\mspace{14mu} p^{\prime}} \in \left\{ {15 +} \right.} \\\left. {{N_{ports}^{CSI}/2},\ldots\mspace{14mu},{15 + N_{ports}^{CSI} - 1}} \right\}\end{matrix}\end{matrix} \right.}\end{matrix}$

In Mathematical expression 1 above, p denotes an aggregated CSI-RS portindex, and p′ denotes a port index in each component CSI-RSconfiguration. Further, N_(ports) ^(CSI) denotes the number of portsincluded in each component CSI-RS configuration, N_(res) ^(CSI) denotesthe total number of component CSI-RS configurations used in CSI-RSaggregation, and i∈{0, 1, . . . , N_(res) ^(CSI)−1} indicates an indexof the component CSI-RS configuration.

Referring to an example of FIG. 11, the relationship as expressed inMathematical expression 1 exists between the antenna port p of theterminal that can recognize 16 CSI-RS ports and the antenna port p′(i.e., port index in the component CSI-RS) of the terminal that canrecognize 16 CSI-RS ports. As an example, it is assumed that CSI-RSconfigurations, such as 1105 and 1106, are configured so that N_(ports)^(CSI) is 8 and N_(res) ^(ports) is 2 with respect to the terminal thatcan recognize 16 CSI-RS ports, and in the case of 1105, i=0, whereas inthe case of 1106, i=1. In this case, if the antenna port of the CSI-RSconfiguration 1104 that a 8-port terminal recognizes is p, the antennaport numbers of 1105 and 1106 are determined as {15, 16, 17, 18, 23, 24,25, 26} in the case of 1105, and are determined as {19, 20, 21, 22, 27,28, 29, 30} in the case of 1106 in accordance with Mathematicalexpression 1.

Referring to Mathematical expression 1, in order to include all antennacomponents of two kinds of polarities in one component CSI-RSconfiguration, the component CSI-RS configuration is decomposed into twosubgroups to perform port numbering. For example, Mathematicalexpression 1 may be understood as a function for cross-pol.

In an example of FIG. 11, it is possible to proceed with a 32-portCSI-RS configuration method for CSI-RS port sharing through extension ofthe above explanation. The base station may configure 4 CSI-RSconfigurations each including 8 CSI-RS ports, such as 1108, 1109, 1110,and 1111 of FIG. 11, for terminals that can recognize 32 CSI-RS ports inall. In this case, the base station performs port numbering based onMathematical expression 1 for port sharing with 8-port and 16-portCSI-RSs.

FIG. 12 is a diagram illustrating CSI-RS resource configuration and portnumbering if CSI-RS RE density for a larger number of CSI-RS ports isdifferent from CSI-RS RE density for a small number of CSI-RS ports in asimilar manner as described above with reference to FIG. 10 according toan embodiment of the present disclosure.

Referring to FIG. 12, respective component CSI-RS configurations 1200,1201, 1202, and 1203 are not transmitted from each PRB or each CSI-RSsubframe, but can be transmitted from a partial PRB group or a partialCSI-RS subframe group in accordance with a configured comb type. FIG. 12illustrates an example in which respective component CSI-RSconfigurations are transmitted from an even PRB or an odd PRB inaccordance with the comb type configuration.

It is assumed that a base station having an antenna array shape of(N1=2, N2=8, P=2) has configured 4 CSI-RS configurations each including8 CSI-RS ports, such as 1211, 1212, 1213, or 1214 of FIG. 12, forterminals that can recognize 32 CSI-RS ports in all. In this case, it isconfigured that the first and third CSI-RS configurations 1211 and 1213are transmitted from an even PRB, and the second and fourth CSI-RSconfigurations 1212 and 1214 are transmitted from an odd PRB. On theother hand, since the existing terminals that can recognize maximally upto 8 or 16 ports are unable to receive (or understand) the CSI-RS portstransmitted from a partial PRB group, the base station can performCSI-RS port sharing with the existing terminal through aggregation orvirtualization of the CSI-RS ports transmitted from the even PRB andCSI-RS ports transmitted from the odd PRB. It can be understood thatCSI-RS virtualization is performed through decomposition of a basestation array, such as 1204 of FIG. 12, into subgroups in the horizontaldirection, in the configuration like this example.

FIG. 13 is a diagram illustrating a base station array being decomposedinto subgroups in a horizontal direction and CSI-RS virtualization isperformed with respect to the decomposed subgroups according to anembodiment of the present disclosure.

Referring to FIG. 13, a base station 1300 may decompose its own arrayinto two kinds of horizontal-direction subgroups 1301 and 1302, and maytransmit the same to an existing terminal 1303 that is unable toentirely understand the antenna array shape of the base station throughdifferent frequency/time comb types.

Referring to FIG. 13, respective component CSI-RSs are transmitted froman odd PRB or an even PRB in accordance with comb type configuration.

For example, the base station can use 16 cross-pol antenna ports thatare adjacent in a horizontal direction, such as 1205 and 1206, forterminals that can recognize maximally 8 CSI-RS ports. In this case, theterminal that can recognize the maximally 8 CSI-RS ports may recognizeCSI-RS ports transmitted for each even PRB from 1205 and CSI-RS portstransmitted for each odd PRB from 1206 as one 8-port CSI-RSconfiguration. For this, the base station has CSI-RS configurations suchas 1205 and 1206 (i.e., it indicates that the base station uses the sameCSI-RS pattern in one RB), but configures to have different comb types.Through this, {19, 20, 21, 22, 35, 36, 37, 38} numbered CSI-RS ports of1212 can be recognized as {15, 16, 17, 18, 19, 20, 21, 22} numberedCSI-RS ports of 1206 through the terminal that receives the 8-portCSI-RSs.

The base station may extend the method for CSI-RS port sharing with theterminals that can recognize maximally 16 CSI-RS ports. In this example,the base station performs CSI-RS virtualization through decomposition ofthe whole array in a horizontal direction, and thus can use avertical-direction array component for the terminals that receive the16-port CSI-RSs. Specifically, CSI-RS ports transmitted from 1207 and1208 are tied into one to configure the first component CSI-RSconfiguration, and CSI-RS ports transmitted from 1209 and 1210 are tiedinto one to configure the second component CSI-RS configuration. Throughthis, the base station may provide CSI-RS ports for (N1=2, N2=4, P=2)antenna array shape to the terminal that can receive maximally 16CSI-RSs.

FIG. 14 is a diagram illustrating CSI-RS resource configuration and portnumbering if CSI-RS RE density for a larger number of CSI-RS ports isdifferent from CSI-RS RE density for a small number of CSI-RS ports in asimilar manner to that as described above with reference to FIG. 10according to an embodiment of the present disclosure.

Referring to FIG. 14, respective component CSI-RS configurations 1400,1401, 1402, and 1403 are not transmitted from each PRB or each CSI-RSsubframe, but can be transmitted from a partial PRB group or a partialCSI-RS subframe group in accordance with a configured comb type. FIG. 14illustrates an example in which respective component CSI-RSconfigurations are transmitted from an even PRB or an odd PRB inaccordance with the comb type configuration.

It is assumed that a base station having an antenna array shape of(N1=2, N2=8, P=2) has configured 4 CSI-RS configurations each including8 CSI-RS ports, such as 1411, 1412, 1413, or 1414 of FIG. 14, forterminals that can recognize 32 CSI-RS ports in all. In this case, it isconfigured that the first and second CSI-RS configurations 1411 and 1412are transmitted from an even PRB, and the third and fourth CSI-RSconfigurations 1413 and 1414 are transmitted from an odd PRB. On theother hand, since the existing terminals that can recognize maximally upto 8 or 16 ports are unable to receive (or understand) the CSI-RS portstransmitted from a partial PRB group, the base station can performCSI-RS port sharing with the existing terminal through aggregation orvirtualization of the CSI-RS ports transmitted from the even PRB andCSI-RSs transmitted from the odd PRB. It can be understood that CSI-RSvirtualization is performed through decomposition of a base stationarray, such as 1404 of FIG. 14, into subgroups in the horizontaldirection, in the configuration like this example.

FIG. 15 is a diagram illustrating a base station array being decomposedinto subgroups in a vertical direction and CSI-RS virtualization isperformed with respect to the decomposed subgroups according to anembodiment of the present disclosure.

Referring to FIG. 15, a base station 1500 may decompose its own arrayinto two kinds of vertical-direction subgroups 1501 and 1502, and maytransmit the same to an existing terminal 1503 that is unable toentirely understand the antenna array shape of the base station throughdifferent frequency/time comb types. Referring to FIG. 15, respectivecomponent CSI-RSs are transmitted from an odd PRB or an even PRB inaccordance with comb type configuration.

For example, the base station can use 16 cross-pol antenna ports thatare adjacent in horizontal and vertical directions, such as 1405 and1406, for terminals that can recognize maximally 8 CSI-RS ports. In thiscase, the terminal that can recognize the maximally 8 CSI-RS ports mayrecognize CSI-RS ports transmitted for each even PRB from 1405 andCSI-RS ports transmitted for each odd PRB from 1406 as one 8-port CSI-RSconfiguration. For this, the base station has CSI-RS configurations suchas 1405 and 1406 (i.e., it indicates that the base station uses the sameCSI-RS pattern in one RB), but configures to have different comb types.Through this, {23, 24, 25, 26, 39, 40, 41, 42} numbered CSI-RS ports of1413 can be recognized as {15, 16, 17, 18, 19, 20, 21, 22} numberedCSI-RS ports of 1406 through the terminal that receives the 8-portCSI-RSs.

The base station may extend the method for CSI-RS port sharing with theterminals that can recognize maximally 16 CSI-RS ports. In this example,the base station performs CSI-RS virtualization through decomposition ofthe whole array in a vertical direction, and thus can use avertical-direction array component for the terminals that receive the16-port CSI-RSs. Specifically, CSI-RS ports transmitted from 1407 and1408 are tied into one to configure the first component CSI-RSconfiguration, and CSI-RS ports transmitted from 1409 and 1410 are tiedinto one to configure the second component CSI-RS configuration. Throughthis, the base station may provide CSI-RS ports for (N1=1, N2=8, P=2)antenna array shape to the terminal that can receive maximally 16CSI-RSs.

FIGS. 16 and 17 are diagrams illustrating port sharing between CSI-RSsusing an orthogonal cover code CDM-4 of length 4. CDM-4 based CSI-RS issupported only to a terminal after release 13, and 12 or 16-port CSI-RSscan be configured according to various embodiments of the presentdisclosure.

Referring to FIGS. 16 and 17, during designing of CDM-4 based CSI-RSport sharing, it is not necessary to consider a CSI-RS pattern up to 8ports, but it is necessary to design a CSI-RS aggregation method over 20ports and a port numbering method based on a 16-port CSI-RS pattern. Onthe other hand, CSI-RS ports of the 12 or 16-port CSI-RS are indexed inaccordance with the port numbering method as expressed in Mathematicalexpression 2 below.p=iN _(ports) ^(CSI) +p′  Mathematical expression 2

In Mathematical expression 2 above, respective variables are the same asthose in Mathematical expression 1. Mathematical expression 2 indicatesthat during 16-port CSI-RS aggregation, individual CSI-RS port indexesof respective CSI-RS configurations are successively increased in theorder of component CSI-RS configuration indexes. On the other hand, inconsideration of 12Tx and 16Tx code book of release 13, the port numbersof 12 or 16-port CSI-RSs are first increased in the horizontal directionwith respect to +45°-pol (or −45°-pol) antennas, and then are increasedin the vertical direction. Thereafter, with respect to −45°-pol (or+45°-pol) antennas with their polarity changed, the port numbers arefirst increased in the horizontal direction, and then are increased inthe vertical direction. The two facts as described above mean thatduring configuration of the 16-port CSI-RSs based on CDM-4, onlyone-polarity antenna component can exist for one component CSI-RSconfiguration. This suggests that new port numbering that is expressedas a function of “antenna array shape and cross-pol” is necessary,unlike the CDM-2 based port numbering that is expressed as a function of“cross-pol” for the CDM-4 based CSI-RS port sharing.

Referring to FIG. 16, the base station having the antenna array shape of(N1=1, N2=8, P=2) (32 antenna ports in total) may configure the CDM-4based 16-port CSI-RSs through aggregation of a plurality of componentCSI-RS configurations. The base station may recognize 16-port antennaarrays having different structures through different aggregation of thecomponent CSI-RS configurations. As an example, the base station mayconfigure 1600 and 1601 of FIG. 16 as the first and second componentCSI-RS configurations, and may transmit 16-port CSI-RSs based on theantenna array shape of (N1=1, N2=8, P=2).

Referring to FIG. 16, if the base station intends to support (N1=1,N2=8, P=2) based 16-port CSI-RSs through component CSI-RS configurationsof 1602 and 1603, it may extend to 1604, 1605, and 1606 to transmit32-port CSI-RSs, and may perform port sharing. In this case, accordingto the port numbering of 1604, 1605, 1606, and 1607, it can be seen thatthe CSI-RS port numbers are successively increased in accordance withthe indexes of the component CSI-RS configurations. Accordingly, in thiscase, it is possible to apply the port numbering method of Mathematicalexpression 2 as it is. This is possible because one component CSI-RSconfiguration wholly includes horizontal-direction antenna ports.

As another example, if the base station intends to support (N1=2, N2=4,P=2) based 16-port CSI-RSs through component CSI-RSs of 1600 and 1601,it may extend to 1608 1609, 1610, and 1611 to transmit 32-port CSI-RSs,and may perform port sharing. In this case, according to the portnumbering of 1608, 1609, 1610, and 1611, it can be seen that the CSI-RSport numbers are not successively increased in accordance with theindexes of the component CSI-RS configurations. This is because onecomponent CSI-RS configuration cannot wholly includehorizontal-direction antenna ports. Accordingly, in this case, it is notpossible to apply the port numbering method of Mathematical expression 2as it is. For example, in order to perform the CDM-4 based CSI-RS portsharing, it is necessary to correct the port numbering method into afunction of not only a cross-pol array structure but also a 2D arrayshape, that is, a function of N1 or N2.

$\begin{matrix}{p = \left\{ \begin{matrix}{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + N_{2} - N_{2}^{Config}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + {2\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + {3\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + \left( {N_{2} - N_{2}^{Config}} \right)} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + {2\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + {3\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}}\end{matrix} \right.} & {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 3}\end{matrix}$

Mathematical expression 3 above refers to a CSI-RS port numbering methodof a new terminal that is extended for the CDM-4 based CSI-RS portsharing. In Mathematical expression 3, p, p′, N_(ports) ^(CSI), N_(res)^(CSI), and i are used as the same meanings as those in Mathematicalexpression 1. N₁ denotes the number of CSI-RS ports (or antenna ports)in the first direction (vertical direction), and N₁ ^(Config) denotesthe number of CSI-RS ports (or antenna ports) in the first direction(vertical direction) included in one component CSI-RS configuration (N₁^(Config) may be the number of CSI-RS ports (or antenna ports) in thefirst direction (or vertical direction) to be recognized by a terminalin the related art that will perform the port sharing). N₂ denotes thenumber of CSI-RS ports (or antenna ports) in the second direction(horizontal direction), and N₂ ^(Config) denotes the number of CSI-RSports (or antenna ports) in the second direction (or horizontaldirection) included in one component CSI-RS configuration (or may be thenumber of CSI-RS ports (or antenna ports) in the second direction (orhorizontal direction) to be recognized by a terminal in the related artthat will perform the port sharing). N₁ ^(Config) and N₂ ^(Config) canbe configured in a dynamic or semi-static manner by physical layersignaling or higher layer signaling, and also can be configured in animplicit manner by a method for determining a specific figure or forselecting a mathematical expression.

As described above, in one aggregated CSI-RS resource, a first half ofCSI-RS ports correspond to antenna ports having the polarity of +45°-pol(or −45°-pol), and the remaining half of CSI-RS ports correspond toantenna ports having the polarity of −45°-pol (or +45°-pol).Accordingly, Mathematical expression 3 enables port numbering to beperformed according to the cross-pol polarity in accordance with thecomponent CSI-RS index condition i<N_(res) ^(CSI)/2 and i≥N_(res) ^(CSI)/2. In addition, since one component CSI-RS configuration can include apart of first and second (or vertical and horizontal)-direction CSI-RSports, it is necessary to additionally consider the number of timesN_(ports) ^(CSI)/N₁ ^(Config) discontinuous port numbering occurs in onecomponent CSI-RS configuration and the size of port index (N₂-N₂^(Config)) to be increased during the discontinuous port numbering.

Detailed examples of the above explanation according to the base stationantenna array shape will be described. If the base station configure1600 and 1601 as first and second component CSI-RS configurations, andconfigures 16-port CSI-RS based on the antenna array shape of (N1=2,N2=4, P=2), the corresponding base station configures 1608, 1609, 1610,and 1611 as the first, third, second, and fourth component CSI-RSconfigurations, respectively, and performs signaling with respect to aterminal that can recognize the antenna array shape of (N1=2, N2=8,P=2). This order is to maintain the aggregated CSI-RS port numberingorder in the 2D cross-pol antenna array as described above.

In this example, each component CSI_RS configuration includes 8 CSI-RSports N_(ports) ^(CSI)=8. Since the number of first-direction (orvertical direction) antenna ports included in one component CSI-RSconfiguration is 2 (N₁ ^(Config)=2), the number of second-direction (orhorizontal direction) antenna ports is N₂=8, and the number ofsecond-direction (or horizontal direction) antenna ports included in onecomponent CSI-RS configuration is N₂ ^(Config)=4, Mathematicalexpression 3 as described above may be managed as Mathematicalexpression 4 below.

$\begin{matrix}{p = \left\{ \begin{matrix}{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + N_{2} - N_{2}^{Config}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + N_{2} - N_{2}^{Config}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}}\end{matrix} \right.} & {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 4}\end{matrix}$

According to Mathematical expression 4 above, in the case of i=0, 1608includes the numbers of antenna ports {15, 16, 17, 18, 23, 24, 25, 26},and in the case of i=1, 1610 includes the numbers of antenna ports {19,20, 21, 22, 27, 28, 29, 30}. Further, in the case of i=2, 1609 includesthe numbers of antenna ports {31, 32, 33, 34, 39, 40, 41, 42}, and inthe case of i=4, 1610 includes the numbers of antenna ports {35, 36, 37,38, 43, 44, 45, 46}.

As another example, a case where a base station has (N1=4, N2=4, P=2)antenna array shape as shown in FIG. 17 will be described. In anenvironment as shown in FIG. 17, the base station may use two methods inorder to configure CDM-4 based 16-port CSI-RS s.

The first method is to configure 16-port CSI-RSs through componentCSI-RS configurations of 1700 and 1701. In this case, the base stationmay extend to 1702, 1703, 1704, and 1705, transmit 32-port CSI-RSs, andperform port sharing. In this case, according to the port numbering of1702, 1703, 1704, and 1705, it can be seen that the CSI-RS port numbersare successively increased in accordance with the indexes of thecomponent CSI-RS configurations. Accordingly, in this case, it ispossible to apply the port numbering method of Mathematical expression 2as it is. This is possible because one component CSI-RS configurationwholly includes horizontal-direction antenna ports.

The second method is to configure 16-port CSI-RSs through componentCSI-RS configurations of 1706 and 1707. In this case, the base stationmay extend to 1708, 1709, 1710, and 1711, transmit 32-port CSI-RSs, andperform port sharing. In this case, according to the port numbering of1708, 1709, 1710, and 1711, it can be seen that the CSI-RS port numbersare not successively increased in accordance with the indexes of thecomponent CSI-RS configurations. This is because one component CSI-RSconfiguration cannot wholly include horizontal-direction antenna ports.Accordingly, in this case, it is not possible to apply the portnumbering method of Mathematical expression 2 as it is.

In this example, each component CSI_RS configuration includes 8 CSI-RSports N_(ports) ^(CSI)=8. Since the number of first-direction (orvertical direction) antenna ports included in one component CSI-RSconfiguration is 4 (N₁ ^(Config)=4), the number of second-direction (orhorizontal direction) antenna ports is N₂=4, the number ofsecond-direction (or horizontal direction) antenna ports included in onecomponent CSI-RS configuration is N₂ ^(Config)=2, and N_(res) ^(CSI)=4,Mathematical expression 3 as described above may be managed asMathematical expression 5 below.

$\begin{matrix}{p = \left\{ \begin{matrix}{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + N_{2} - N_{2}^{Config}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + {2\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}i} + {3\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} < {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {15,\ldots\mspace{14mu},\ {15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\ {and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + \left( {N_{2} - N_{2}^{Config}} \right)} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + {2\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{2N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}} \\{p^{\prime} + {\frac{N_{ports}^{CSI}}{N_{1}^{Config}}\left( {i + {N_{res}^{CSI}/2}} \right)} + {3\left( {N_{2} - N_{2}^{Config}} \right)}} & {{{for}\mspace{14mu} p^{\prime}} \in {{\left\{ {{15 + \frac{3N_{ports}^{CSI}}{N_{1}^{Config}}},\ldots\mspace{20mu},{15 + N_{ports}^{CSI} - 1}} \right\}\mspace{14mu}{and}\mspace{14mu} i} \geq {N_{res}^{CSI}/2}}}\end{matrix} \right.} & {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 5}\end{matrix}$

In this case, if i=0 is substituted for, it is possible to determine theantenna port number of 1708, and if i=1 is substituted for, it ispossible to determine the antenna port number of 1709. Further, if i=2is substituted for, it is possible to determine the antenna port numberof 1710, and if i=3 is substituted for, it is possible to determine theantenna port number of 1711.

As another port numbering method for CSI-RS port sharing, there may be amethod for supporting only Mathematical expression 2. In this case, inorder to support continuous port numbering, the CSI-RS configurationshould be limited to satisfy the following conditions.

1) The number of antenna ports N₂ ^(Config) in the second direction (orhorizontal direction) included in one component CSI-RS configuration(i.e., the number of horizontal-direction antenna ports in an antennaarray shape having a smaller size for port sharing) is equal to thenumber of second-direction antenna ports N₂ of a base station antennaarray (i.e., the number of horizontal-direction antenna ports in anantenna array shape having a larger size for port sharing).

2) If condition 1) is not satisfied and N₂ ^(Config) is smaller than N₂,the number of first-direction (or vertical-direction) antenna ports N₁included in one component CSI-RS configuration is N₁=1.

One of methods for this is to make engagement so as to mean N₂^(Config)=N₂. Table 3 below indicates values of N₁ and N₂ for signalingto release 13 terminals. This may be understood by terminals afterrelease 14 as N₁ ^(Config) and N₂ ^(Config). According to the abovecondition 1), the base station may adjust N₂ values of release 13terminals, that is, N₂ ^(Config), in accordance with N₂ configurationfor the terminal after release 14 for CDM-4 based CSI-RS port sharing.For example, if N₂ for the terminal after release 14 is N₂=4, the basestation configures this as N₁ ^(Config)=2, N₂ ^(Config)=4. For example,in this case, the number of CSI-RS ports of the release 13 terminal forthe port sharing is 16. Further, as another example, if N₂ for theterminal after release 14 is N₂=2, the base station configures this asN₁ ^(Config)=2, N₂ ^(Config)=3. For example, in this case, the number ofCSI-RS ports of the release 13 terminal for the port sharing is 12. Theabove example indicates that the number of CSI-RS ports configured tothe release 13 terminal may be determined in accordance with N₂configured to terminals after release 14.

TABLE 3 Number of CSI-RS antenna ports, P (N₁, N₂) (O₁, O₂) 8 (2, 2) (4,4), (8, 8) 12 (2, 3) (8, 4), (8, 8) (3, 2) (8, 4), (4, 4) 16 (2, 4) (8,4), (8, 8) (4, 2) (8, 4), (4, 4) (8, 1) (4, —), (8, —)

If a CSI-RS resource for terminals after release 14 includes componentCSI_RS configurations having different port numbers, crosstalk may occurin port numbering according to the above-described embodiments. As anexample, if the number of CSI-RS ports included in the k^(th) componentCSI-RS configuration is N_(k)=8, and the number of CSI-RS ports includedin the first component CSI-RS configuration is N₁=4, the CSI-RS portnumbering for the CSI-RS port sharing may not have a regular structureas expressed in the above-described mathematical expressions. In orderto avoid this problem, if the respective component CSI-RS configurationsinclude different numbers of CSI-RS ports, that is, N_(k)≠N₁, engagementcan be made so that N₂ for terminals of release 13 or heretofore, thatis, N₂ ^(Config), follows N₂ of the first component CSI-RS configuration(where, k=1) configured to terminals after release 14.

Here, it should be noted that the number of CSI-RS ports according tothe CSI-RS RE pattern specified according to the component CSI-RSconfiguration may differ from the number of CSI-RS ports included in theactual component CSI-RS configuration to be transmitted. For example,the RE pattern of the first CSI-RS configuration is determined by 8-portCSI-RS configuration, and the CSI-RS is transmitted using the 8 CSI-RSports according to the RE pattern. In contrast, the RE pattern of thesecond CSI-RS configuration is determined by 8-port CSI-RSconfiguration, and the CSI-RS can be transmitted using only 2 or 4CSI-RS ports. This is to support the CSI-RS port sharing with a smallernumber of CSI-RSs and to constantly maintain the CDM pattern for alarger number of CSI-RSs at the same time.

In the above-described embodiments, it is mainly assumed that the basestation has 32 antenna ports. However, a similar method, such aschanging of the port number of a reference CSI-RS configuration oraggregation of the reference CSI-RS configuration including thedifferent number of ports can also be adopted. Further, in theabove-described embodiments, for convenience in explanation, terms“horizontal direction” and “vertical direction” have been used. However,it is apparent that they are generalized to be understood as the firstdirection and the second direction.

FIG. 18 is a flowchart illustrating an order of operations of a terminalaccording to an embodiment of the present disclosure.

Referring to FIG. 18, at operation 1810, a terminal receivesconfiguration information for CSI-RS configuration. The configurationinformation may include CSI-RS configuration information according toany one of the above-described embodiments. Further, the terminal mayconfirm at least one of the number of CSI-RS ports, transmission timingof CSI-RSs and resource locations, and transmission power informationbased on the received configuration information.

Thereafter, at operation 1820, the terminal receives feedbackconfiguration information based on at least one CSI-RS. If the CSI-RS isreceived, the terminal, at operation 1830, estimates a channel between atransmission antenna of a base station and a reception antenna of theterminal using the received CSI-RS. Then, at operation 1840, theterminal generates RI, PMI and/or CQI that correspond to feedbackinformation using the received feedback configuration and predefinedcodebook based on the estimated channel. In this case, the estimatedchannel may include a virtual channel that is added based on the CSI-RSconfiguration information.

Thereafter, at operation 1850, the terminal transmits the feedbackinformation to the base station in the certain feedback timing inaccordance with the feedback configuration of the base station.

FIG. 19 is a flowchart illustrating an order of operations of a basestation according to an embodiment of the present disclosure.

Referring to FIG. 19, a base station determines CSI-RS transmissionconfiguration according to at least one of the above-describedembodiments, generates CSI-RS configuration information, and thetransmit CSI-RS configuration information for measuring a channel to aterminal at operation 1910. The configuration information may include atleast one of the number of CSI-RS ports, transmission timing of CSI-RSsand resource locations, and transmission power information.

Thereafter, at operation 1920, the base station transmits to theterminal feedback configuration information based on at least oneCSI-RS. Thereafter, the base station transmits to the terminal CSI-RSsconfigured according to the CSI-RS configuration information. Theterminal estimates a channel for each antenna port, and estimatesadditional channel for a virtual resource based on this. The terminalgenerates and transmits to the base station PMI, RI and/or CQI thatcorrespond to the feedback information at operation 1930. Accordingly,the base station receives the feedback information from the terminal ina certain timing, and uses the feedback information in determining thechannel state between the terminal and the base station.

FIG. 20 is a block diagram illustrating an internal structure of aterminal according to an embodiment of the present disclosure.

Referring to FIG. 20, a terminal includes a transceiver unit 2010 and acontroller 2020. The transceiver unit 201 transmits and receives datafrom an outside (e.g., base station). Here, the transceiver unit 2010may transmit feedback information to a base station under the control ofthe controller 2020. The controller 2020 controls states and operationsof all constituent elements constituting the terminal. Specifically, thecontroller 2020 generates the feedback information according toinformation allocated from the base station. Further, the controller2020 controls the transceiver unit 2010 to feed the generated channelinformation back to the base station according to timing informationallocated from the base station. For this, the controller 2020 mayinclude a channel estimation unit 2030. The channel estimation unit 2030determines the necessary feedback information through the CSI-RSs andfeedback allocation information received from the base station, andestimates a channel using the received CSI-RSs based on the feedbackinformation.

FIG. 20 illustrates that the terminal includes the transceiver unit 2010and the controller 2020. However, the configuration of the terminal isnot limited thereto, but may further include various configurationsaccording to the function performed in the terminal. For example, theterminal may further include a display unit displaying the current stateof the terminal, an input unit receiving an input of a signal forfunction performing from a user, and a storage unit storing therein datagenerated in the terminal.

Further, although it is illustrated that the channel estimation unit2030 is included in the controller 2020, but is not limited thereto. Thecontroller 2020 may control the transceiver unit 2010 to receive fromthe base station configuration information for at least one referencesignal resource. Further, the controller 2020 may control thetransceiver unit 2010 to measure at least one reference signal, and toreceive from the base station feedback configuration information forgenerating the feedback information according to the result of themeasurement.

Further, the controller 2020 may measure at least one reference signalreceived through the transceiver unit 2010, and may generate thefeedback information according to the feedback configurationinformation. Further, the controller 2020 may control the transceiverunit 2010 to transmit the generated feedback information to the terminalin a feedback timing according to the feedback configurationinformation.

Further, the controller 2020 may receive CSI-RSs from the base station,generate feedback information based on the received CSI-RSs, andtransmit the generated feedback information to the base station. In thiscase, the controller 2020 may select a precoding matrix with referenceto the relationship between the antenna port groups of the base and theterminal itself.

Further, the controller 2020 may receive the CSI-RSs from the basestation, generate feedback information based on the received CSI-RSs,and transmit the generated feedback information to the base station. Inthis case, the controller 2020 may select a precoding matrix withreference to the relationship between the antenna port groups of thebase and the terminal itself. Further, the controller 2020 may receivefeedback configuration information from the base station, receive theCSI-RSs from the base station, and transmit the generated feedbackinformation to the base station. Further, the controller 2020 mayreceive the feedback configuration information corresponding to therespective antenna port groups and additional feedback configurationinformation based on the relationship between the antenna port groups.

FIG. 21 is a block diagram illustrating an internal structure of a basestation according to an embodiment of the present disclosure.

Referring to FIG. 21, a base station includes a controller 2110 and atransceiver unit 2120.

The controller 2110 controls states and operations of all constituentelements constituting the base station. Specifically, the controller2110 allocates to a terminal CSI-RS resources for channel estimation ofthe terminal, and allocates feedback resources and feedback timing tothe terminal.

For this, the controller 2110 may further include a resource allocationunit 2130. Further, the controller 2110 allocates feedback configurationand feedback timing so as to prevent collision of feedbacks from severalterminals, and receives and analyses the feedback information configuredin the corresponding timing. The transceiver unit 2120 transmits andreceives data, a reference signal, and feedback information from theterminal. Here, the transceiver unit 2120 transmits the CSI-RSs to theterminal through the allocated resources under the control of thecontroller 2110, and receive a feedback of channel information from theterminal. It is illustrated that the resource allocation unit 2130 isincluded in the controller 2110, but is not limited thereto.

The controller 2110 may control the transceiver unit 2120 to transmitconfiguration information for at least one reference signal to theterminal, or may generate the at least one reference signal. Further,the controller 2110 may control the transceiver unit 2120 to transmitthe feedback configuration information for generating the feedbackinformation according to the measurement result to the terminal.Further, the controller 2110 may control the transceiver unit 2120 totransmit the at least one reference signal to the terminal and toreceive the feedback information that is transmitted from the terminalin the feedback timing according to the feedback configurationinformation.

Further, the controller 2110 may transmit the feedback configurationinformation to the terminal, transmit the CSI-RSs to the terminal, andreceive the generated feedback information from the terminal based onthe feedback configuration information and the CSI-RS. In this case, thecontroller 2110 may transmit the feedback configuration informationcorresponding to the antenna port groups of the base station andadditional feedback configuration information based on the relationshipbetween the antenna port groups. Further, the controller 2110 maytransmit beamformed CSI-RSs to the terminal based on the feedbackinformation, and may receive the feedback information generated based onthe CSI-RSs from the terminal.

According to the embodiments of the present disclosure as describedabove, the base station having a large number of transmission antennasof a 2D antenna array structure can prevent excessive feedback resourceallocation for transmitting CSI-RSs and increase of channel estimationcomplexity of a terminal, and the terminal can effectively measurechannels of a large number of transmission antennas and can report tothe base station feedback information configured through themeasurement.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a channel stateinformation reference signal (CSI-RS) in a communication system, themethod comprising: transmitting, to a terminal, CSI-RS configurationinformation on a plurality of CSI-RS resource sets, configuration ofeach of the plurality of CSI-RS resource sets including a list of CSI-RSresource indices and each of the CSI-RS resource indices beingassociated with at least one CSI-RS antenna port; transmitting, to theterminal, CSI-RSs corresponding to the plurality of CSI-RS resource setsaccording to the CSI-RS configuration information; and receiving, fromthe terminal, feedback information associated with the CSI-RSs, whereinconfiguration on a CSI-RS resource includes antenna port informationindicating a number of the at least one CSI-RS antenna port, frequencyresource allocation information indicating a density of a CSI-RScorresponding to the CSI-RS resource in a frequency domain, and timinginformation for the CSI-RS, and wherein CSI-RSs corresponding to a firstCSI-RS resource set and CSI-RSs corresponding to a second CSI-RSresource set are transmitted in different time-frequency resources. 2.The method of claim 1, wherein the CSI-RS configuration informationincludes offset information for the CSI-RS resource set, and the offsetinformation is applied to at least one of CSI-RS resource included inthe CSI-RS resource set.
 3. The method of claim 1, wherein resources ofCSI-RSs corresponding to the first CSI-RS resource set and resources ofCSI-RSs corresponding to the second CSI-RS resource set aretime-division multiplexed.
 4. The method of claim 1, wherein resourcesof CSI-RSs corresponding to the first CSI-RS resource set and resourcesof CSI-RSs corresponding to the second CSI-RS resource set arefrequency-division multiplexed.
 5. The method of claim 1, wherein thedensity of the CSI-RS corresponds to a number of CSI-RS resourceelements in a plurality of physical resource blocks for the at least oneCSI-RS antenna port.
 6. A method for receiving a channel stateinformation reference signal (CSI-RS) in a communication system, themethod comprising: receiving, from a base station, CSI-RS configurationinformation on a plurality of CSI-RS resource sets, configuration ofeach of the plurality of CSI-RS resource sets including a list of CSI-RSresource indices and each of the CSI-RS resource indices beingassociated with at least one CSI-RS antenna port; receiving, from thebase station, CSI-RSs corresponding to the plurality of CSI-RS resourcesets based on the CSI-RS configuration information; and transmitting, tothe base station, feedback information obtained based on the receivedCSI-RSs, wherein configuration on a CSI-RS resource includes antennaport information indicating a number of the at least one CSI-RS antennaport, frequency resource allocation information indicating a density ofa CSI-RS corresponding to the CSI-RS resource in a frequency domain, andtiming information for the CSI-RS, and wherein CSI-RSs corresponding toa first CSI-RS resource set and CSI-RSs corresponding to a second CSI-RSresource set are received in different time-frequency resources.
 7. Themethod of claim 6, wherein the CSI-RS configuration information includesoffset information for a CSI-RS resource set, and the offset informationis applied to at least one of CSI-RS resource included in the CSI-RSresource set.
 8. The method of claim 6, wherein resources of CSI-RSscorresponding to the first CSI-RS resource set and resources of CSI-RSscorresponding to the second CSI-RS resource set are time-divisionmultiplexed.
 9. The method of claim 6, wherein resources of CSI-RSscorresponding to the first CSI-RS resource set and resources of CSI-RSscorresponding to the second CSI-RS resource set are frequency-divisionmultiplexed.
 10. The method of claim 6, wherein the density of theCSI-RS corresponds to a number of CSI-RS resource elements in aplurality of physical resource blocks for the at least one CSI-RSantenna port.
 11. A base station in a communication system, the basestation comprising: a transceiver; and a controller coupled with thetransceiver and configured to: transmit, to a terminal, channel stateinformation reference signal (CSI-RS) configuration information on aplurality of CSI-RS resource sets, configuration of each of theplurality of CSI-RS resource sets including a list of CSI-RS resourceindices and each of the CSI-RS resource indices being associated with atleast one CSI-RS antenna port, transmit, to the terminal, CSI-RSscorresponding to the plurality of CSI-RS resource sets according to theCSI-RS configuration information, and receive, from the terminal,feedback information associated with the CSI-RSs, wherein configurationon a CSI-RS resource includes antenna port information indicating anumber of the at least one CSI-RS antenna port, frequency resourceallocation information indicating a density of a CSI-RS corresponding tothe CSI-RS resource in a frequency domain, and timing information forthe CSI-RS, and wherein CSI-RSs corresponding to a first CSI-RS resourceset and CSI-RSs corresponding to a second CSI-RS resource set aretransmitted in different time-frequency resources.
 12. The base stationof claim 11, wherein the CSI-RS configuration information includesoffset information for the CSI-RS resource set, and the offsetinformation is applied to at least one of CSI-RS resource included inthe CSI-RS resource set.
 13. The base station of claim 11, whereinresources of CSI-RSs corresponding to the first CSI-RS resource set andresources of CSI-RSs corresponding to the second CSI-RS resource set aretime-division multiplexed.
 14. The base station of claim 11, whereinresources of CSI-RSs corresponding to the first CSI-RS resource set andresources of CSI-RSs corresponding to the second CSI-RS resource set arefrequency-division multiplexed.
 15. The base station of claim 11,wherein the density of the CSI-RS corresponds to a number of CSI-RSresource elements in a plurality of physical resource blocks for the atleast one CSI-RS antenna port.
 16. A terminal in a communication system,the terminal comprising: a transceiver; and a controller coupled withthe transceiver and configured to: receive, from a base station, channelstate information reference signal (CSI-RS) configuration information ona plurality of CSI-RS resource sets, configuration of each of theplurality of CSI-RS resource sets including a list of CSI-RS resourceindices and each of the CSI-RS resource indices being associated with atleast one CSI-RS antenna port, receive, from the base station, CSI-RSscorresponding to the plurality of CSI-RS resource sets based on theCSI-RS configuration information, and transmit, to the base station,feedback information obtained based on the received CSI-RSs, whereinconfiguration on a CSI-RS resource includes antenna port informationindicating a number of the at least one CSI-RS antenna port, frequencyresource allocation information indicating a density of a CSI-RScorresponding to the CSI-RS resource in a frequency domain, and timinginformation for the CSI-RS, and wherein CSI-RSs corresponding to a firstCSI-RS resource set and CSI-RSs corresponding to a second CSI-RSresource set are received in different time-frequency resources.
 17. Theterminal of claim 16, wherein the CSI-RS configuration informationincludes offset information for a CSI-RS resource set, and the offsetinformation is applied to at least one of CSI-RS resource included inthe CSI-RS resource set.
 18. The terminal of claim 16, wherein resourcesof CSI-RSs corresponding to the first CSI-RS resource set and resourcesof CSI-RSs corresponding to the second CSI-RS resource set aretime-division multiplexed.
 19. The terminal of claim 16, whereinresources of CSI-RSs corresponding to the first CSI-RS resource set andresources of CSI-RSs corresponding to the second CSI-RS resource set arefrequency-division multiplexed.
 20. The terminal of claim 16, whereinthe density of the CSI-RS corresponds to a number of CSI-RS resourceelements in a plurality of physical resource blocks for the at least oneCSI-RS antenna port.